login
A356861
a(n) is the number of nonzero digits in the product of the first n numbers not divisible by 5.
4
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
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. A356859 (number of zero digits), A356860 (number of digits).
Sequence in context: A306733 A085207 A179969 * A327717 A085203 A251104
KEYWORD
nonn,base
AUTHOR
Stefano Spezia, Sep 01 2022
STATUS
approved