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

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

Author

Jon E. Schoenfield, May 27 2018

Keywords

• nonn
• base

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

• Jon E. Schoenfield, Table of n, a(n) for n = 1..10000 (first 1000 terms from Alois P. Heinz)

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