cp's OEIS Frontend

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

%I A305231 #20 Jan 28 2023 12:01:45
%S A305231 0,1,4,9,10,16,25,36,40,49,64,81,90,100,121,160,250,252,360,400,403,
%T A305231 484,490,574,640,736,765,810,900,976,1000,1008,1089,1207,1210,1300,
%U A305231 1458,1462,1600,1612,1729,1855,1936,1944,2268,2296,2430,2500,2520,2668,2701
%N A305231 Numbers that are the product of some integer and its digit reversal.
%C A305231 Terms of A061205, sorted in increasing order, with duplicates removed.
%H A305231 Jon E. Schoenfield, <a href="/A305231/b305231.txt">Table of n, a(n) for n = 1..10000</a> (first 1000 terms from Alois P. Heinz)
%e A305231 12*21 = 252, so 252 is a term.
%e A305231 156*651 = 101556, so 101556 is a term. (It can also be written as 273*372; see A203924.)
%p A305231 a:= proc(n) option remember; local k, d; for k from 1+a(n-1) do
%p A305231       for d in numtheory[divisors](k) do if k = d*(s-> parse(cat(
%p A305231       seq(s[-i], i=1..length(s)))))(""||d) then return k fi od od
%p A305231     end: a(1):=0:
%p A305231 seq(a(n), n=1..60);  # _Alois P. Heinz_, May 27 2018
%t A305231 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 *)
%o A305231 (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
%Y A305231 Cf. A061205, A203924.
%Y A305231 Cf. A325148 (squares), A359981 (nonsquares).
%K A305231 nonn,base
%O A305231 1,3
%A A305231 _Jon E. Schoenfield_, May 27 2018