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.

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A061205 a(n) = n times R(n) where R(n) (A004086) is the digit reversal of n.

Original entry on oeis.org

0, 1, 4, 9, 16, 25, 36, 49, 64, 81, 10, 121, 252, 403, 574, 765, 976, 1207, 1458, 1729, 40, 252, 484, 736, 1008, 1300, 1612, 1944, 2296, 2668, 90, 403, 736, 1089, 1462, 1855, 2268, 2701, 3154, 3627, 160, 574, 1008, 1462, 1936, 2430, 2944, 3478, 4032, 4606
Offset: 0

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Author

Amarnath Murthy, Apr 21 2001

Keywords

Comments

Every third term is divisible by 9, no other term is divisible by 3. - Alonso del Arte, Mar 04 2013

Examples

			a(10) = 10 = 10 * 01.
a(11) = 121 = 11 * 11.
a(12) = 252 = 12 * 21.
a(13) = 403 = 13 * 31.

Links

Crossrefs

Cf. A004086, A203924 (triple repetitions).

Programs

Extensions

Corrected and extended by Patrick De Geest, Jun 04 2001

A305231 Numbers that are the product of some integer and its digit reversal.

Original entry on oeis.org

0, 1, 4, 9, 10, 16, 25, 36, 40, 49, 64, 81, 90, 100, 121, 160, 250, 252, 360, 400, 403, 484, 490, 574, 640, 736, 765, 810, 900, 976, 1000, 1008, 1089, 1207, 1210, 1300, 1458, 1462, 1600, 1612, 1729, 1855, 1936, 1944, 2268, 2296, 2430, 2500, 2520, 2668, 2701
Offset: 1

Views

Author

Jon E. Schoenfield, May 27 2018

Keywords

Comments

Terms of A061205, sorted in increasing order, with duplicates removed.

Examples

			12*21 = 252, so 252 is a term.
156*651 = 101556, so 101556 is a term. (It can also be written as 273*372; see A203924.)

Links

Crossrefs

Cf. A061205, A203924.
Cf. A325148 (squares), A359981 (nonsquares).

Programs

  • Maple
    a:= proc(n) option remember; local k, d; for k from 1+a(n-1) do
      for d in numtheory[divisors](k) do if k = d*(s-> parse(cat(
      seq(s[-i], i=1..length(s)))))(""||d) then return k fi od od
    end: a(1):=0:
seq(a(n), n=1..60);  # Alois P. Heinz, May 27 2018
  • Mathematica
    a={0}; h=-1; For[k=0, k<=2701, k++, For[m=1, m<=DivisorSigma[0, k], m++, d=Divisors[k]; If[k/Part[d, m] == FromDigits[Reverse[IntegerDigits[Part[d, m]]]] && k>h , AppendTo[a, k]; h=k]]]; a (* Stefano Spezia, Jan 28 2023 *)
  • PARI
    isok(n) = if (n==0, return (1), fordiv(n, d, if (n/d == fromdigits(Vecrev(digits(d))), return (1))); return (0)); \\ Michel Marcus, May 28 2018
Showing 1-2 of 2 results.

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

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