A125059 - OEIS

A125059

Number of digits in n!!.

1, 1, 1, 1, 1, 2, 2, 3, 3, 3, 4, 5, 5, 6, 6, 7, 8, 8, 9, 9, 10, 11, 11, 12, 13, 13, 14, 15, 16, 16, 17, 18, 19, 19, 20, 21, 22, 22, 23, 24, 25, 26, 27, 27, 28, 29, 30, 31, 32, 32, 33, 34, 35, 36, 37, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57

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OFFSET

0,6

LINKS

Table of n, a(n) for n=0..76.

FORMULA

a(n) = A055642(A006882(n)).

EXAMPLE

a(5) = 2 because 5!! = 5*3*1 = 15.

MAPLE

a:= n-> length(doublefactorial(n)):

seq(a(n), n=0..76); # Alois P. Heinz, Sep 28 2023