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

Author

Hieronymus Fischer, Apr 01 2012

Keywords

• base
• nonn

Comments

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.

Examples

			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).
		

Links

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

Crossrefs

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

Programs

Mathematica

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

Formula

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

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