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

0,6

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

SFACT:= proc(n) local i, j, k; for k from 1 by 1 to n do i:=k; j:=k-2; while j >0 do i:=i*j; j:=j-2; od: j:=0; while i>0 do i:=trunc(i/10); j:=j+1; od; print(j) od; end: SFACT(100);
# second Maple program:
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 *)

Crossrefs

Cf. A006882, A034886, A055642.

Sequence in context: A300068 A194202 A261224 * A369611 A029112 A348336

Adjacent sequences: A125056 A125057 A125058 * A125060 A125061 A125062

Keyword

easy,nonn,base

Author

Paolo P. Lava and Giorgio Balzarotti, Jan 08 2007

Extensions

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

Status

approved