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 A120625 #9 Nov 21 2013 12:48:59
%S A120625 15,20,42,77,88,104,126,140,153,156,170,187,190,204,209,210,220,228,
%T A120625 231,238,240,266,299,308,312,322,368,420,429,435,440,442,450,460,464,
%U A120625 468,476,483,493,496,510,527,551,558,561,580,589,600,609,620,624,651,665
%N A120625 Numbers n such that the n-th Catalan number C(2n,n)/(n+1) is divisible by 3n.
%C A120625 Equivalently, numbers n such that the n-th central binomial coefficient C(2n,n) is divisible by 3n(n+1). - _Joel B. Lewis_, Jan 07 2008
%H A120625 Harvey P. Dale, <a href="/A120625/b120625.txt">Table of n, a(n) for n = 1..1000</a>
%t A120625 fQ[n_] := fQ[n_] := IntegerQ[ Binomial[2n, n]/(3n(n + 1))]; Select[ Range@681, fQ@# &]
%t A120625 With[{nn=700},Transpose[Select[Thread[{CatalanNumber[Range[nn]],Range[ nn]}],Divisible[#[[1]],3#[[2]]]&]][[2]]] (* _Harvey P. Dale_, Apr 30 2012 *)
%Y A120625 Subset of A104847, Cf. A120623.
%K A120625 nonn
%O A120625 1,1
%A A120625 _Robert G. Wilson v_, Jun 19 2006
%E A120625 Definition corrected by _Joel B. Lewis_, Apr 30 2009