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

Offset: 0

Author

Paolo P. Lava and Giorgio Balzarotti, Jan 08 2007

Keywords

• easy
• nonn
• base

Examples

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

Crossrefs

Cf. A006882, A034886, A055642.

Programs

Maple

a:= n-> length(doublefactorial(n)):
seq(a(n), n=0..76);  # Alois P. Heinz, Sep 28 2023

Mathematica

IntegerLength[Range[80]!!] (* Harvey P. Dale, Mar 23 2018 *)

Formula

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

Extensions

a(0)=1 prepended by Georg Fischer, Sep 28 2023