A356860 a(n) is the number of digits in the product of the first n numbers not divisible by 5.

1, 1, 1, 1, 2, 3, 4, 4, 5, 6, 7, 9, 10, 11, 12, 13, 15, 16, 17, 19, 20, 22, 23, 24, 26, 27, 29, 30, 32, 33, 35, 37, 38, 40, 41, 43, 45, 46, 48, 50, 51, 53, 55, 57, 58, 60, 62, 64, 65, 67, 69, 71, 73, 74, 76, 78, 80, 82, 84, 85, 87, 89, 91, 93, 95, 97, 99, 101, 103

Offset

0,5

Links

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

Formula

a(n) = A055642(A356858(n)).

Mathematica

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

Prog

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

Crossrefs

Cf. A047201, A055642, A356858.

Cf. A356859 (number of zero digits), A356861 (number of nonzero digits).

Sequence in context: A268084 A261085 A017876 * A017865 A317143 A351520

Adjacent sequences: A356857 A356858 A356859 * A356861 A356862 A356863

Keyword

nonn,base

Author

Stefano Spezia, Sep 01 2022

Status

approved