This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A125059 #16 Jun 11 2025 14:31:22 %S A125059 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, %T A125059 16,17,18,19,19,20,21,22,22,23,24,25,26,27,27,28,29,30,31,32,32,33,34, %U A125059 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 %N A125059 Number of digits in n!!. %F A125059 a(n) = A055642(A006882(n)). %e A125059 a(5) = 2 because 5!! = 5*3*1 = 15. %p A125059 a:= n-> length(doublefactorial(n)): %p A125059 seq(a(n), n=0..76); # _Alois P. Heinz_, Sep 28 2023 %t A125059 IntegerLength[Range[80]!!] (* _Harvey P. Dale_, Mar 23 2018 *) %Y A125059 Cf. A006882, A034886, A055642. %K A125059 easy,nonn,base %O A125059 0,6 %A A125059 _Paolo P. Lava_ and _Giorgio Balzarotti_, Jan 08 2007 %E A125059 a(0)=1 prepended by _Georg Fischer_, Sep 28 2023