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A356859
a(n) is the number of zero digits in the product of the first n numbers not divisible by 5.
4
0, 0, 0, 0, 0, 0, 2, 1, 0, 0, 2, 1, 0, 1, 1, 1, 0, 2, 1, 0, 0, 2, 4, 1, 2, 2, 2, 6, 5, 2, 3, 5, 4, 2, 5, 3, 4, 6, 4, 3, 8, 3, 3, 4, 8, 9, 6, 3, 5, 9, 6, 10, 9, 7, 4, 11, 10, 10, 8, 13, 9, 5, 8, 8, 11, 7, 8, 10, 13, 11, 10, 12, 11, 13, 13, 16, 6, 16, 10, 21, 17
OFFSET
0,7
FORMULA
a(n) = A055641(A356858(n)).
MATHEMATICA
Table[Count[IntegerDigits[Product[Floor[(5i-1)/4], {i, n}]], 0], {n, 0, 80}]
PROG
(Python)
from math import prod
def a(n): return str(prod((5*k-1)//4 for k in range(1, n+1))).count("0")
print([a(n) for n in range(81)]) # Michael S. Branicky, Sep 01 2022
CROSSREFS
Cf. A356860 (number of digits), A356861 (number of nonzero digits).
Sequence in context: A294019 A123721 A077618 * A085863 A220354 A344478
KEYWORD
nonn,base
AUTHOR
Stefano Spezia, Sep 01 2022
STATUS
approved