OFFSET
1,3
COMMENTS
a(n) is the number of digits in double factorial of odd numbers (see A001147).
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
For n = 7, (2*n-1)!! = 13!! = 135135 and the number of digits is 6.
MAPLE
seq(1 + ilog10(doublefactorial(2*n-1)), n=1..100); # Robert Israel, Jan 15 2024
MATHEMATICA
a[n_] := IntegerLength[(2 n - 1)!!]; Array[a, 65] (* Amiram Eldar, Oct 23 2020 *)
PROG
(Sage) floor((log(factorial(2 * n) / ((2 ** n) * factorial(n))) / log(10))) + 1
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Jeremias M. Gomes, Oct 23 2020
STATUS
approved