A356861 - OEIS

%I #7 Sep 04 2022 12:38:51

%S 1,1,1,1,2,3,2,3,5,6,5,8,10,10,11,12,15,14,16,19,20,20,19,23,24,25,27,

%T 24,27,31,32,32,34,38,36,40,41,40,44,47,43,50,52,53,50,51,56,61,60,58,

%U 63,61,64,67,72,67,70,72,76,72,78,84,83,85,84,90,91,91,90

%N a(n) is the number of nonzero digits in the product of the first n numbers not divisible by 5.

%F a(n) = A055640(A356858(n)).

%t Table[Length[Select[IntegerDigits[Product[Floor[(5i-1)/4], {i,n}]], Positive]], {n,0,68}]

%o (Python)

%o from math import prod

%o def a(n): s = str(prod((5*k-1)//4 for k in range(1, n+1))); return len(s) - s.count("0")

%o print([a(n) for n in range(69)]) # _Michael S. Branicky_, Sep 01 2022

%Y Cf. A047201, A055640, A356858.

%Y Cf. A356859 (number of zero digits), A356860 (number of digits).

%K nonn,base

%O 0,5

%A _Stefano Spezia_, Sep 01 2022