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 A120390 #21 May 19 2021 11:50:46
%S A120390 1,2,3,8,6,12,6,15,18,15,18,18,18,18,18,18,36,45,45,36,45,45,36,54,63,
%T A120390 45,72,45,72,72,90,90,90,81,108,81,108,81,126,90,108,108,144,81,144,
%U A120390 90,135,117,144,126,153,108,180,135,180,135,171,180,180,171,198,180,198
%N A120390 Sum of digits of double factorial numbers.
%C A120390 If n > 10, then 9 divides a(n). - _Michel Lagneau_, Dec 22 2011
%H A120390 Harvey P. Dale, <a href="/A120390/b120390.txt">Table of n, a(n) for n = 1..1000</a>
%F A120390 a(n) = A007953(A006882(n)) - _Eric Chen_, Jun 13 2018
%e A120390 5!! = 5*3*1 = 15 --> 1+5 = 6
%p A120390 P:=proc(n) local i,j,k,t1,t2; for i from 1 by 1 to n do j:=i; k:=i-2; while k>0 do j:=j*k; k:=k-2; od; t1:=j; t2:=0; while t1 <> 0 do t2:= t2+(t1 mod 10); t1 := floor(t1/10); od; print(t2); od; end: P(100);
%t A120390 Table[Total[IntegerDigits[n!!]],{n,70}] (* _Harvey P. Dale_, May 19 2021 *)
%Y A120390 Cf. A004152, A006882, A007953.
%K A120390 easy,nonn,base
%O A120390 1,2
%A A120390 _Paolo P. Lava_ and _Giorgio Balzarotti_, Jun 30 2006