A210885 -id:A210885 - cp's OEIS frontend

A210884 Dates after Jan 01 1000 which are palindromic when they are written according to the ISO-8601-format YYYYMMDD.

10011001, 10100101, 10111101, 10200201, 10211201, 10300301, 10400401, 10500501, 10600601, 10700701, 10800801, 10900901, 11011011, 11100111, 11111111, 11200211, 11211211, 11300311, 11400411, 11500511, 11600611, 11700711, 11800811, 11900911, 12011021, 12100121, 12111121, 12200221, 12211221, 12300321, 12400421, 12500521, 12600621, 12700721, 12800821, 12900921

Offset: 1

Hieronymus Fischer, Apr 01 2012

There are exactly 331 such palindromic dates between Jan 1 1000 and Dec 31 9999 (see b-file for the complete list).
Dates palindromic in the YYYYMMDD format are also palindromic in the MMDDYYYY format. Consequently, this sequence represents the same dates as A210893.
See A210883 for the number of days after Jan 1 1000 to get such a palindromic date.
The first palindromic dates after 'Jan 01 2000' are 20011002, 20100102, 20111102, 20200202, 20211202, 20300302, 20400402, 20500502, 20600602, 20700702, 20800802, 20900902, 21011012 which are the 44th, 45th, ... 56th ... dates of the original sequence.

			The first palindromic date in YYYYMMDD format after 'Jan 01 1000' is a(1)=10011001 (= 'Oct 01 1001' = 'Jan 01 1000' + A210883(1) days);
The 47th palindromic date in YYYYMMDD format after 'Jan 01 1000' is a(47)=20200202 (= 'Feb 02 2020' = 'Jan 01 1000' + A210883(47) days).
The last (331st) palindromic date in YYYYMMDD format before the year 10000 is a(331)=92900929 (= 'Sep 29 9290' = 'Jan 01 1000' + A210883(331) days).

Hieronymus Fischer, Table of n, a(n) for n = 1..331

Cf. A210883, A210885 - A210895, A106605, A107273, A107275.

Select[StringDelete[#,"-"]&/@(DateString[#,"ISODate"]&/@DateRange[{1000,1,1},{9999,12,31}]),PalindromeQ]//ToExpression  (* Harvey P. Dale, Dec 24 2023 *)

a(n)=YYYYMMDD_date('Jan 1 1000' + A210883(n)).

n-th date after 'Jan 1 2000' = a(43+n).

A210886 Dates after Jan 01 1000 in chronological order which are palindromic when they are written in the format DDMMYYYY. Leading zeros of the terms are suppressed.

Original entry on oeis.org

10011001, 20011002, 30011003, 1011010, 11011011, 21011012, 31011013, 2011020, 12011021, 22011022, 3011030, 13011031, 23011032, 4011040, 14011041, 24011042, 5011050, 15011051, 25011052, 6011060, 16011061, 26011062, 7011070, 17011071, 27011072, 8011080, 18011081, 28011082, 9011090, 19011091

Offset: 1

Hieronymus Fischer, Apr 01 2012

There are exactly 335 such palindromic dates between Jan 1 1000 and Dec 31 9999 (see b-file for the complete list).
See A210885 for the number of days after 'Jan 1 1000' to get such a palindromic date.
The first palindromic dates after 'Jan 01 2000' are 10022001, 20022002, 1022010, 11022011, 21022012, 2022020, 12022021, 22022022, 3022030, 13022031, 23022032, 4022040, 14022041, 24022042, 5022050, ... which are the 62nd, 63rd, ... 76th ... dates of the original sequence.

			The first palindromic date in DDMMYYYY format after 'Jan 01 1000' is a(1)=10011001 (= 'Jan 10 1001' = 'Jan 01 1000' + A210885(1) days);
The fourth palindromic date in DDMMYYYY format after 'Jan 01 1000' is a(4)=1011010=01011010 (= 'Jan 01 1010' = 'Jan 01 1000' + A210885(4) days);
The 66th palindromic date in DDMMYYYY format after 'Jan 01 1000' is a(66)=21022012 (= 'Feb 21 2012' = 'Jan 01 1000' + A210885(66) days)
The last (335th) palindromic date in DDMMYYYY format before the year 10000 is a(335)=29099092 (= 'Sep 29 9092' = 'Jan 01 1000' + A210885(335) days).

Hieronymus Fischer, Table of n, a(n) for n = 1..335

Cf. A210883 - A210885, A210887 - A210895, A106605, A107273, A107275.

a(n)=DDMMYYYY_date('Jan 1 1000' + A210885(n)).

n-th date after 'Jan 1 2000' = a(61+n).

A213182 Numbers which may represent a date in "condensed European notation" DDMMYY.

Original entry on oeis.org

10100, 10101, 10102, 10103, 10104, 10105, 10106, 10107, 10108, 10109, 10110, 10111, 10112, 10113, 10114, 10115, 10116, 10117, 10118, 10119, 10120, 10121, 10122, 10123, 10124, 10125, 10126, 10127, 10128, 10129, 10130, 10131, 10132, 10133, 10134, 10135, 10136, 10137, 10138, 10139, 10140

Offset: 1

M. F. Hasler, Feb 27 2013

The "may" in the definition should clarify that, e.g., 290200 is in the sequence since it may represent a date, but not necessarily in any century.
The sequence is finite, the largest term is a(36525)=311299.
There are 366*25 + 365*75 = 36525 possible dates. - Giovanni Resta, Feb 28 2013

			a(1)=10100 represents e.g., Jan 01 1900 or Jan 01 2000.
a(100)=10199 (for Jan 01 1999) is followed by a(101)=10200 (for Feb 01 2000).
a(1200)=11299 (for Dec 01 1999) is followed by a(1201)=20100 (for Jan 02 2000).
The sequence becomes more interesting after the term 281299, since then the numbers DD02YY drop out for DD > 29 and for DD = 29 depending on YY.

Cf. A213184; A106605, A107273, A107275; A210883, A210884, A210885.

A213184 Numbers which may represent a date in "condensed American notation" MMDDYY.

Original entry on oeis.org

10100, 10101, 10102, 10103, 10104, 10105, 10106, 10107, 10108, 10109, 10110, 10111, 10112, 10113, 10114, 10115, 10116, 10117, 10118, 10119, 10120, 10121, 10122, 10123, 10124, 10125, 10126, 10127, 10128, 10129, 10130, 10131, 10132, 10133, 10134, 10135, 10136, 10137, 10138, 10139, 10140

Offset: 1

M. F. Hasler, Feb 28 2013

The "may" in the definition should clarify that, e.g., 22900 is in the sequence since it may represent a date (Feb. 29), but not necessarily in any century (e.g., in 2000 but not in 1900), but 22900+k is present only for k=0 (mod 4).

The sequence is finite, with 366*25 + 365*75 terms, cf. comment from G. Resta in A213182. The largest term is a(36525)=123199.

			a(1)=10100 represents, e.g., Jan 01 1900 (or Jan 01 2000).
a(100)=10199 (for Jan 01 1999) is followed by a(101)=10200 (for Jan 02 2000).
a(3100)=13199 (for Jan 31 1999) is followed by a(3101)=20100 (for Feb 01 2000).

Cf. A213182, A106605, A107273, A107275; A210883, A210884, A210885.

cp's OEIS Frontend

A210884 Dates after Jan 01 1000 which are palindromic when they are written according to the ISO-8601-format YYYYMMDD.

Views

Author

Keywords

Comments

Examples

Links

Crossrefs

Programs

Mathematica

Formula

A210886 Dates after Jan 01 1000 in chronological order which are palindromic when they are written in the format DDMMYYYY. Leading zeros of the terms are suppressed.

Views

Author

Keywords

Comments

Examples

Links

Crossrefs

Formula

A213182 Numbers which may represent a date in "condensed European notation" DDMMYY.

Views

Author

Keywords

Comments

Examples

Crossrefs

A213184 Numbers which may represent a date in "condensed American notation" MMDDYY.

Views

Author

Keywords

Comments

Examples

Crossrefs