cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-3 of 3 results.

A227409 Prime numbers representing a date in "condensed American notation" MMDDYY.

Original entry on oeis.org

10103, 10111, 10133, 10139, 10141, 10151, 10159, 10163, 10169, 10177, 10181, 10193, 10211, 10223, 10243, 10247, 10253, 10259, 10267, 10271, 10273, 10289, 10301, 10303, 10313, 10321, 10331, 10333, 10337, 10343, 10357, 10369, 10391, 10399, 10427, 10429, 10433
Offset: 1

Views

Author

Shyam Sunder Gupta, Sep 22 2013

Keywords

Comments

For February, the number of days will be 28 only, as the year cannot be a leap year if MMDDYY is to be a prime number.
The sequence is finite, with 3379 terms. The largest term is a(3379)=123191.

Examples

			a(1)=10103 is prime and represents a date in MMDDYY format as 010103.

Links

Crossrefs

Cf. A227407, A213184.

Programs

  • Mathematica
    t = {}; Do[If[m < 8, If[OddQ[m], b = 31, If[m == 2, b = 28, b = 30]],If[OddQ[m], b = 30, b = 31]]; Do[a = 100 d + y + 10000 m;If[PrimeQ[a], AppendTo[t, a]], {d, 1, b}], {m, 1, 12}, {y, 1, 99}]; Union[t]

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

Views

Author

M. F. Hasler, Feb 27 2013

Keywords

Comments

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

Examples

			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.

Crossrefs

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

A227410 Palindromic prime numbers representing a date in "condensed American notation" MMDDYY.

Original entry on oeis.org

10301, 10501, 10601, 11311, 11411, 12421, 12721, 12821, 30103, 30203, 30403, 30703, 30803, 31013, 31513, 32323, 32423, 70207, 70507, 70607, 71317, 71917, 72227, 72727, 73037, 90709, 91019
Offset: 1

Views

Author

Shyam Sunder Gupta, Sep 22 2013

Keywords

Comments

For February, the number of days will be 28 only, as the year cannot be a leap year if MMDDYY is to be a prime number.
The sequence is finite, with 27 terms. The largest term is a(27)=91019.

Examples

			a(1)=10301 is palindromic prime and represents a date in MMDDYY format as 010301.

Crossrefs

Cf. A213184, A227409, A227411.

Programs

  • Mathematica
    palindromicQ[n_] := TrueQ[IntegerDigits[n] == Reverse[IntegerDigits[n]]]; t = {}; Do[If[m < 8, If[OddQ[m], b = 31, If[m == 2, b = 28, b = 30]], If[OddQ[m], b = 30, b = 31]]; Do[a = 100 d + y + 10000 m; If[PrimeQ[a] && palindromicQ[a], AppendTo[t, a]], {d, 1, b}], {m, 1,
   12}, {y, 1, 99}]; Union[t]
Showing 1-3 of 3 results.

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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