A356861 a(n) is the number of nonzero digits in the product of the first n numbers not divisible by 5.

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, 24, 27, 31, 32, 32, 34, 38, 36, 40, 41, 40, 44, 47, 43, 50, 52, 53, 50, 51, 56, 61, 60, 58, 63, 61, 64, 67, 72, 67, 70, 72, 76, 72, 78, 84, 83, 85, 84, 90, 91, 91, 90

Offset

0,5

Links

Table of n, a(n) for n=0..68.

Formula

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

Mathematica

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

Prog

(Python)
from math import prod
def a(n): s = str(prod((5*k-1)//4 for k in range(1, n+1))); return len(s) - s.count("0")
print([a(n) for n in range(69)]) # Michael S. Branicky, Sep 01 2022

Crossrefs

Cf. A047201, A055640, A356858.

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

Sequence in context: A306733 A085207 A179969 * A327717 A085203 A251104

Adjacent sequences: A356858 A356859 A356860 * A356862 A356863 A356864

Keyword

nonn,base

Author

Stefano Spezia, Sep 01 2022

Status

approved