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 A304335 #15 May 12 2018 14:42:56
%S A304335 1,1,3,6,6,18,18,18,18,36,45,45,36,63,72,72,90,90,108,108,126,108,144,
%T A304335 144,135,144,153,180,180,171,180,198,198,189,216,243,243,234,252,225,
%U A304335 243,261,252,297,306,333,360,324,342,342,315,360,369,378,396,387,387,414
%N A304335 Sum of digits of (2*n-1)!!.
%H A304335 Seiichi Manyama, <a href="/A304335/b304335.txt">Table of n, a(n) for n = 0..1000</a>
%F A304335 a(n) = A007953(A001147(n)).
%p A304335 a:= n-> add(i, i=convert(doublefactorial(2*n-1), base, 10)):
%p A304335 seq(a(n), n=0..60); # _Alois P. Heinz_, May 11 2018
%o A304335 (PARI) {a(n) = sumdigits((2*n)!/(n!*2^n))}
%Y A304335 Cf. A001147, A004152.
%K A304335 nonn,base
%O A304335 0,3
%A A304335 _Seiichi Manyama_, May 11 2018