cp's OEIS Frontend

A338505 Number of positive integers less than n with the same product of decimal digits as n.

%I A338505 #11 Apr 14 2022 09:28:59
%S A338505 0,0,0,0,0,0,0,0,0,0,1,1,1,1,1,1,1,1,1,1,2,2,2,2,0,0,0,0,0,2,2,3,2,1,
%T A338505 0,1,0,0,0,3,3,3,2,1,0,1,0,0,0,4,2,1,1,1,0,0,0,0,0,5,4,3,2,2,1,1,0,0,
%U A338505 0,6,2,1,1,1,1,1,0,0,0,7,4,2,3,1,1,1,1,0,0,8
%N A338505 Number of positive integers less than n with the same product of decimal digits as n.
%F A338505 a(n) = |{0 < j < n : A007954(j) = A007954(n)}|.
%e A338505 a(22) = 2 because A007954(22) = 4 and also A007954(4) = A007954(14) = 4.
%t A338505 Table[Length[Select[Range[n - 1], Times @@ IntegerDigits@# == Times @@ IntegerDigits@n &]], {n, 90}]
%o A338505 (PARI) a(n)={my(t=vecprod(digits(n))); sum(k=1, n-1, vecprod(digits(k))==t)} \\ _Andrew Howroyd_, Oct 31 2020
%Y A338505 Cf. A007954, A138471, A254524.
%K A338505 nonn,base
%O A338505 1,21
%A A338505 _Ilya Gutkovskiy_, Oct 31 2020
%E A338505 Definition clarified by _Ilya Gutkovskiy_, Apr 14 2022