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.

A028865 Primes that when squared gives numbers with digits in nondecreasing order.

Original entry on oeis.org

2, 3, 5, 7, 13, 17, 37, 67, 83, 107, 167, 337, 367, 383, 587, 1667, 166667, 333337, 333367, 333667, 336667, 666667, 33333667, 33666667, 66666667, 333333367, 666666667, 1666666667, 3336666667, 33333366667, 66666666667, 166666666667, 333333333367, 333333333667, 333336666667
Offset: 1

Views

Author

Patrick De Geest

Keywords

Crossrefs

Cf. A028866, A028868, A028869.

Extensions

Title changed to reflect terms by Sean A. Irvine, Feb 12 2020
a(26)-a(35) from Giovanni Resta, Feb 13 2020

A028866 Squares of primes having digits in nondecreasing order.

Original entry on oeis.org

4, 9, 25, 49, 169, 289, 1369, 4489, 6889, 11449, 27889, 113569, 134689, 146689, 344569, 2778889, 27777888889, 111113555569, 111133556689, 111333666889, 113344668889, 444444888889, 1111133355666889, 1133444466888889
Offset: 1

Views

Author

Patrick De Geest

Keywords

Comments

What is the rate of growth of this sequence?

Crossrefs

Subsequence of A052043.
Cf. A028865, A028868, A028869.

Programs

  • Mathematica
    Select[Prime[Range[100]]^2, IntegerDigits[#] == Sort[IntegerDigits[#]] &] (* Alonso del Arte, Jan 18 2017 *)
  • PARI
    is(n)=my(d=digits(n));d==vecsort(d) && issquare(n,&n) && isprime(n) \\ Charles R Greathouse IV, Jun 05 2013

Extensions

Title changed to reflect terms by Sean A. Irvine, Feb 12 2020

A028869 Squares of primes with digits in nonascending order.

Original entry on oeis.org

4, 9, 841, 961
Offset: 1

Views

Author

Patrick De Geest

Keywords

Comments

No other solutions below 4 * 10^18 (probably finite). - Dec 15 1999

Examples

			961 = 31^2 is in the sequence since its digits (9, 6, 1) are in descending order.
1369 = 37^2 is not in the sequence, since its digits in descending order are: 9, 6, 3, 1.

Crossrefs

Cf. A028868, A028865, A028866.

Programs

  • Mathematica
    Select[Prime[Range[100]]^2, IntegerDigits[#] == Sort[IntegerDigits[#], Less] &] (* Alonso del Arte, Aug 12 2016 *)

Extensions

Offset changed by Altug Alkan, Sep 09 2016
Name clarified by Jon E. Schoenfield, Oct 27 2023
Showing 1-3 of 3 results.

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

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