A305231 - OEIS

%I #20 Jan 28 2023 12:01:45

%S 0,1,4,9,10,16,25,36,40,49,64,81,90,100,121,160,250,252,360,400,403,

%T 484,490,574,640,736,765,810,900,976,1000,1008,1089,1207,1210,1300,

%U 1458,1462,1600,1612,1729,1855,1936,1944,2268,2296,2430,2500,2520,2668,2701

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

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

%H 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 12*21 = 252, so 252 is a term.

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

%p a:= proc(n) option remember; local k, d; for k from 1+a(n-1) do

%p       for d in numtheory[divisors](k) do if k = d*(s-> parse(cat(

%p       seq(s[-i], i=1..length(s)))))(""||d) then return k fi od od

%p     end: a(1):=0:

%p seq(a(n), n=1..60);  # _Alois P. Heinz_, May 27 2018

%t 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 (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 Cf. A061205, A203924.

%Y Cf. A325148 (squares), A359981 (nonsquares).

%K nonn,base

%O 1,3

%A _Jon E. Schoenfield_, May 27 2018