Palindromic dates in the YYYYMMDD format @ Things Of Interest

Today, 20211202 (2nd December 2021), is a palindrome in the YYYYMMDD format. It is the 83rd of what will ultimately be 366 palindromic dates in this format.

The first of these was 01011010 (10th October 101).
The most recent one was 20200202 (2nd February 2020).
The next one is 20300302 (2nd March 2030).
The last one will be 92900929 (29th September 9290).

Dates of this format come in waves separated by huge gaps. There were no palindromic dates of this format between 13800831 (31st August 1380) and 20011002 (2nd October 2001). Between 2001 and 22900922 (22nd September 2290), we can expect about one every ten years. Then a similarly huge gap appears until 30011003 (3rd October 3001). This repeating millennium-long pattern, of a few centuries of about one per decade followed by many more centuries of nothing, has been visible since the epoch, and will continue fairly regularly until the year number hits five digits.

(For the record, the best date format is not YYYYMMDD but YYYY-MM-DD, which is always totally unambiguous and allows lexicographical sorting. Dates in this format are never palindromic, due to the placement of the hyphens.)

Full list

Every possible birthday appears in this listing exactly once! To figure out yours,

take your birthday, say 16th February
express it in MMDD format: 0216
add four digits on the front to turn that into a palindrome: 61200216
look for 61200216 (16th February 6120) in the table.

#	YYYYMMDD	DDs MMMM YYYY	Days until next
1	01011010	10th October 101	3014
2	01100110	10th January 110	669
3	01111110	10th November 111	3014
4	01200210	10th February 120	669
5	01211210	10th December 121	3012
6	01300310	10th March 130	3684
7	01400410	10th April 140	3682
8	01500510	10th May 150	3684
9	01600610	10th June 160	3682
10	01700710	10th July 170	3684
11	01800810	10th August 180	3683
12	01900910	10th September 190	4057
13	02011020	20th October 201	3014
14	02100120	20th January 210	669
15	02111120	20th November 211	3014
16	02200220	20th February 220	669
17	02211220	20th December 221	3012
18	02300320	20th March 230	3684
19	02400420	20th April 240	3682
20	02500520	20th May 250	3684
21	02600620	20th June 260	3682
22	02700720	20th July 270	3684
23	02800820	20th August 280	3683
24	02900920	20th September 290	4057
25	03011030	30th October 301	3014
26	03100130	30th January 310	669
27	03111130	30th November 311	3683
28	03211230	30th December 321	3012
29	03300330	30th March 330	3684
30	03400430	30th April 340	3682
31	03500530	30th May 350	3684
32	03600630	30th June 360	3682
33	03700730	30th July 370	3684
34	03800830	30th August 380	3683
35	03900930	30th September 390	223164
36	10011001	1st October 1001	3014
37	10100101	1st January 1010	669
38	10111101	1st November 1011	3014
39	10200201	1st February 1020	669
40	10211201	1st December 1021	3012
41	10300301	1st March 1030	3684
42	10400401	1st April 1040	3682
43	10500501	1st May 1050	3684
44	10600601	1st June 1060	3682
45	10700701	1st July 1070	3684
46	10800801	1st August 1080	3683
47	10900901	1st September 1090	4057
48	11011011	11th October 1101	3014
49	11100111	11th January 1110	669
50	11111111	11th November 1111	3014
51	11200211	11th February 1120	669
52	11211211	11th December 1121	3012
53	11300311	11th March 1130	3684
54	11400411	11th April 1140	3682
55	11500511	11th May 1150	3684
56	11600611	11th June 1160	3682
57	11700711	11th July 1170	3684
58	11800811	11th August 1180	3683
59	11900911	11th September 1190	4058
60	12011021	21st October 1201	3014
61	12100121	21st January 1210	669
62	12111121	21st November 1211	3014
63	12200221	21st February 1220	669
64	12211221	21st December 1221	3012
65	12300321	21st March 1230	3684
66	12400421	21st April 1240	3682
67	12500521	21st May 1250	3684
68	12600621	21st June 1260	3682
69	12700721	21st July 1270	3684
70	12800821	21st August 1280	3683
71	12900921	21st September 1290	4057
72	13011031	31st October 1301	3014
73	13100131	31st January 1310	4352
74	13211231	31st December 1321	3012
75	13300331	31st March 1330	7366
76	13500531	31st May 1350	7366
77	13700731	31st July 1370	3684
78	13800831	31st August 1380	226847
79	20011002	2nd October 2001	3014
80	20100102	2nd January 2010	669
81	20111102	2nd November 2011	3014
82	20200202	2nd February 2020	669
83	20211202	2nd December 2021	3012
84	20300302	2nd March 2030	3684
85	20400402	2nd April 2040	3682
86	20500502	2nd May 2050	3684
87	20600602	2nd June 2060	3682
88	20700702	2nd July 2070	3684
89	20800802	2nd August 2080	3683
90	20900902	2nd September 2090	4057
91	21011012	12th October 2101	3014
92	21100112	12th January 2110	669
93	21111112	12th November 2111	3014
94	21200212	12th February 2120	669
95	21211212	12th December 2121	3012
96	21300312	12th March 2130	3684
97	21400412	12th April 2140	3682
98	21500512	12th May 2150	3684
99	21600612	12th June 2160	3682
100	21700712	12th July 2170	3684
101	21800812	12th August 2180	3683
102	21900912	12th September 2190	4057
103	22011022	22nd October 2201	3014
104	22100122	22nd January 2210	669
105	22111122	22nd November 2211	3014
106	22200222	22nd February 2220	669
107	22211222	22nd December 2221	3012
108	22300322	22nd March 2230	3684
109	22400422	22nd April 2240	3682
110	22500522	22nd May 2250	3684
111	22600622	22nd June 2260	3682
112	22700722	22nd July 2270	3684
113	22800822	22nd August 2280	3683
114	22900922	22nd September 2290	259698
115	30011003	3rd October 3001	3014
116	30100103	3rd January 3010	669
117	30111103	3rd November 3011	3014
118	30200203	3rd February 3020	669
119	30211203	3rd December 3021	3012
120	30300303	3rd March 3030	3684
121	30400403	3rd April 3040	3682
122	30500503	3rd May 3050	3684
123	30600603	3rd June 3060	3682
124	30700703	3rd July 3070	3684
125	30800803	3rd August 3080	3683
126	30900903	3rd September 3090	4057
127	31011013	13th October 3101	3014
128	31100113	13th January 3110	669
129	31111113	13th November 3111	3014
130	31200213	13th February 3120	669
131	31211213	13th December 3121	3012
132	31300313	13th March 3130	3684
133	31400413	13th April 3140	3682
134	31500513	13th May 3150	3684
135	31600613	13th June 3160	3682
136	31700713	13th July 3170	3684
137	31800813	13th August 3180	3683
138	31900913	13th September 3190	4058
139	32011023	23rd October 3201	3014
140	32100123	23rd January 3210	669
141	32111123	23rd November 3211	3014
142	32200223	23rd February 3220	669
143	32211223	23rd December 3221	3012
144	32300323	23rd March 3230	3684
145	32400423	23rd April 3240	3682
146	32500523	23rd May 3250	3684
147	32600623	23rd June 3260	3682
148	32700723	23rd July 3270	3684
149	32800823	23rd August 3280	3683
150	32900923	23rd September 3290	259698
151	40011004	4th October 4001	3014
152	40100104	4th January 4010	669
153	40111104	4th November 4011	3014
154	40200204	4th February 4020	669
155	40211204	4th December 4021	3012
156	40300304	4th March 4030	3684
157	40400404	4th April 4040	3682
158	40500504	4th May 4050	3684
159	40600604	4th June 4060	3682
160	40700704	4th July 4070	3684
161	40800804	4th August 4080	3683
162	40900904	4th September 4090	4057
163	41011014	14th October 4101	3014
164	41100114	14th January 4110	669
165	41111114	14th November 4111	3014
166	41200214	14th February 4120	669
167	41211214	14th December 4121	3012
168	41300314	14th March 4130	3684
169	41400414	14th April 4140	3682
170	41500514	14th May 4150	3684
171	41600614	14th June 4160	3682
172	41700714	14th July 4170	3684
173	41800814	14th August 4180	3683
174	41900914	14th September 4190	4057
175	42011024	24th October 4201	3014
176	42100124	24th January 4210	669
177	42111124	24th November 4211	3014
178	42200224	24th February 4220	669
179	42211224	24th December 4221	3012
180	42300324	24th March 4230	3684
181	42400424	24th April 4240	3682
182	42500524	24th May 4250	3684
183	42600624	24th June 4260	3682
184	42700724	24th July 4270	3684
185	42800824	24th August 4280	3683
186	42900924	24th September 4290	259698
187	50011005	5th October 5001	3014
188	50100105	5th January 5010	669
189	50111105	5th November 5011	3014
190	50200205	5th February 5020	669
191	50211205	5th December 5021	3012
192	50300305	5th March 5030	3684
193	50400405	5th April 5040	3682
194	50500505	5th May 5050	3684
195	50600605	5th June 5060	3682
196	50700705	5th July 5070	3684
197	50800805	5th August 5080	3683
198	50900905	5th September 5090	4057
199	51011015	15th October 5101	3014
200	51100115	15th January 5110	669
201	51111115	15th November 5111	3014
202	51200215	15th February 5120	669
203	51211215	15th December 5121	3012
204	51300315	15th March 5130	3684
205	51400415	15th April 5140	3682
206	51500515	15th May 5150	3684
207	51600615	15th June 5160	3682
208	51700715	15th July 5170	3684
209	51800815	15th August 5180	3683
210	51900915	15th September 5190	4058
211	52011025	25th October 5201	3014
212	52100125	25th January 5210	669
213	52111125	25th November 5211	3014
214	52200225	25th February 5220	669
215	52211225	25th December 5221	3012
216	52300325	25th March 5230	3684
217	52400425	25th April 5240	3682
218	52500525	25th May 5250	3684
219	52600625	25th June 5260	3682
220	52700725	25th July 5270	3684
221	52800825	25th August 5280	3683
222	52900925	25th September 5290	259698
223	60011006	6th October 6001	3014
224	60100106	6th January 6010	669
225	60111106	6th November 6011	3014
226	60200206	6th February 6020	669
227	60211206	6th December 6021	3012
228	60300306	6th March 6030	3684
229	60400406	6th April 6040	3682
230	60500506	6th May 6050	3684
231	60600606	6th June 6060	3682
232	60700706	6th July 6070	3684
233	60800806	6th August 6080	3683
234	60900906	6th September 6090	4057
235	61011016	16th October 6101	3014
236	61100116	16th January 6110	669
237	61111116	16th November 6111	3014
238	61200216	16th February 6120	669
239	61211216	16th December 6121	3012
240	61300316	16th March 6130	3684
241	61400416	16th April 6140	3682
242	61500516	16th May 6150	3684
243	61600616	16th June 6160	3682
244	61700716	16th July 6170	3684
245	61800816	16th August 6180	3683
246	61900916	16th September 6190	4057
247	62011026	26th October 6201	3014
248	62100126	26th January 6210	669
249	62111126	26th November 6211	3014
250	62200226	26th February 6220	669
251	62211226	26th December 6221	3012
252	62300326	26th March 6230	3684
253	62400426	26th April 6240	3682
254	62500526	26th May 6250	3684
255	62600626	26th June 6260	3682
256	62700726	26th July 6270	3684
257	62800826	26th August 6280	3683
258	62900926	26th September 6290	259698
259	70011007	7th October 7001	3014
260	70100107	7th January 7010	669
261	70111107	7th November 7011	3014
262	70200207	7th February 7020	669
263	70211207	7th December 7021	3012
264	70300307	7th March 7030	3684
265	70400407	7th April 7040	3682
266	70500507	7th May 7050	3684
267	70600607	7th June 7060	3682
268	70700707	7th July 7070	3684
269	70800807	7th August 7080	3683
270	70900907	7th September 7090	4057
271	71011017	17th October 7101	3014
272	71100117	17th January 7110	669
273	71111117	17th November 7111	3014
274	71200217	17th February 7120	669
275	71211217	17th December 7121	3012
276	71300317	17th March 7130	3684
277	71400417	17th April 7140	3682
278	71500517	17th May 7150	3684
279	71600617	17th June 7160	3682
280	71700717	17th July 7170	3684
281	71800817	17th August 7180	3683
282	71900917	17th September 7190	4058
283	72011027	27th October 7201	3014
284	72100127	27th January 7210	669
285	72111127	27th November 7211	3014
286	72200227	27th February 7220	669
287	72211227	27th December 7221	3012
288	72300327	27th March 7230	3684
289	72400427	27th April 7240	3682
290	72500527	27th May 7250	3684
291	72600627	27th June 7260	3682
292	72700727	27th July 7270	3684
293	72800827	27th August 7280	3683
294	72900927	27th September 7290	259698
295	80011008	8th October 8001	3014
296	80100108	8th January 8010	669
297	80111108	8th November 8011	3014
298	80200208	8th February 8020	669
299	80211208	8th December 8021	3012
300	80300308	8th March 8030	3684
301	80400408	8th April 8040	3682
302	80500508	8th May 8050	3684
303	80600608	8th June 8060	3682
304	80700708	8th July 8070	3684
305	80800808	8th August 8080	3683
306	80900908	8th September 8090	4057
307	81011018	18th October 8101	3014
308	81100118	18th January 8110	669
309	81111118	18th November 8111	3014
310	81200218	18th February 8120	669
311	81211218	18th December 8121	3012
312	81300318	18th March 8130	3684
313	81400418	18th April 8140	3682
314	81500518	18th May 8150	3684
315	81600618	18th June 8160	3682
316	81700718	18th July 8170	3684
317	81800818	18th August 8180	3683
318	81900918	18th September 8190	4057
319	82011028	28th October 8201	3014
320	82100128	28th January 8210	669
321	82111128	28th November 8211	3014
322	82200228	28th February 8220	669
323	82211228	28th December 8221	3012
324	82300328	28th March 8230	3684
325	82400428	28th April 8240	3682
326	82500528	28th May 8250	3684
327	82600628	28th June 8260	3682
328	82700728	28th July 8270	3684
329	82800828	28th August 8280	3683
330	82900928	28th September 8290	259698
331	90011009	9th October 9001	3014
332	90100109	9th January 9010	669
333	90111109	9th November 9011	3014
334	90200209	9th February 9020	669
335	90211209	9th December 9021	3012
336	90300309	9th March 9030	3684
337	90400409	9th April 9040	3682
338	90500509	9th May 9050	3684
339	90600609	9th June 9060	3682
340	90700709	9th July 9070	3684
341	90800809	9th August 9080	3683
342	90900909	9th September 9090	4057
343	91011019	19th October 9101	3014
344	91100119	19th January 9110	669
345	91111119	19th November 9111	3014
346	91200219	19th February 9120	669
347	91211219	19th December 9121	3012
348	91300319	19th March 9130	3684
349	91400419	19th April 9140	3682
350	91500519	19th May 9150	3684
351	91600619	19th June 9160	3682
352	91700719	19th July 9170	3684
353	91800819	19th August 9180	3683
354	91900919	19th September 9190	4058
355	92011029	29th October 9201	3014
356	92100129	29th January 9210	669
357	92111129	29th November 9211	3014
358	92200229	29th February 9220	669
359	92211229	29th December 9221	3012
360	92300329	29th March 9230	3684
361	92400429	29th April 9240	3682
362	92500529	29th May 9250	3684
363	92600629	29th June 9260	3682
364	92700729	29th July 9270	3684
365	92800829	29th August 9280	3683
366	92900929	29th September 9290

Intervals

Intervals between one palindromic date and the next show some repetition. Here is how frequently different intervals appear:

Interval (days)	Count
669	59
3012	31
3014	60
3682	60
3683	31
3684	91
4057	16
4058	5
4352	1
7366	2
223164	1
226847	1
259698	7
Total	365

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Discussion (16)

2021-12-02 00:45:09 by qntm:

See you all in nine-and-a-bit years.

2021-12-02 06:48:31 by hobbs:

And sometimes (well, twice a century in the centuries that have palindromes at all), a gap of one year and ten months works, incrementing both of the middle digits.

2021-12-02 18:04:37 by laverya:

The prevalence of 669 is interesting - almost 20% of 'days until next' is that number.

2021-12-02 18:23:38 by SubmanUK:

Another great post from DataGenetics! … wait where am i? :)

2021-12-02 21:32:23 by Boter:

New life goal: live life long enough to reach my birthday palindrome.

2021-12-02 21:45:22 by P:

Less than 300 years till my birthday is a palindrome! Guess I'm one of the lucky ones.

2021-12-03 05:31:36 by tanamr:

Can't wait til we get to the palindromic year 19391 (which is also 1969)

2021-12-08 18:33:56 by mszegedy:

Despite the following table of interval counts, it took me a while to understand what the "days until next" column was for. If anyone else is wondering: it's the length of the interval between that row's palindromic date and the next row's, in days. (Before that, my best guess was the interval between 2021 Dec 2 and that date, which was obviously nonsense, and caused me great confusion.

2021-12-08 18:34:17 by mszegedy:

)

2021-12-17 07:38:37 by Ingvar:

Well, both YYYYMMDD and YYYY-MM-DD sort lexicographically (the "-" does not influence the ordering, as all YYYY-MM-DD dates will have the "-" in the same place). But, yes, given a choice between YYYYMMDD and YYYY-MM-DD, I will choose the latter every time. But if the choice is between MM/DD/YYYY or YYYY/DD/MM and YYYYMMDD, I will pick YYYYMMDD without a second's hesitation. I would also posit that it is allowable to ignore the separators when judging for palindromeness (and, likewise, capitalisation), otherwise "A man, a plan, a canal, Panama!" would not be a palindrome and it is pretty much the epitome of standard examples of one in the English language. But, yeah, somewhat harder to write a palindrome checker for.

2022-01-14 02:01:13 by wroughage:

Is there significance to the total being 365? Kind of a weird total. (I know it's 365+ d/y)

2022-01-14 02:03:18 by qntm:

Yes, for each of the 366 possible days in the year there is a palindromic date, and between the 366 palindromic dates there are 365 intervals.

2022-01-21 17:06:47 by MrRandom:

Interesting to see.

2022-01-22 04:58:09 by David:

This is great. Thank you!

2022-03-23 01:53:24 by Soyfish:

That's really cool

2022-05-09 15:35:37 by iewqr:

qntm,I love your creations! From this article,scp antimeme division to hatetris.Keep the good work!