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A125059
Number of digits in n!!.
0
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
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
KEYWORD
easy,nonn,base
AUTHOR
EXTENSIONS
a(0)=1 prepended by Georg Fischer, Sep 28 2023
STATUS
approved