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 A120622 #9 Aug 14 2025 15:06:59 %S A120622 4,24,40,72,304,480,560,1032,1248,1376,1440,1632,1696,2128,2320,2400, %T A120622 2576,2720,3360,3520,4104,4176,4240,4320,4368,4704,4896,5056,5280, %U A120622 5568,5664,5824,6160,6240,6592,6848,6976,7200,7360,7744,8064,8200,8240,8272 %N A120622 Numbers k such that the k-th Catalan number C(2k, k)/(k + 1) is divisible by k/2 but not divisible by k. %H A120622 Chai Wah Wu, <a href="/A120622/b120622.txt">Table of n, a(n) for n = 1..10000</a> %t A120622 fQ[n_] := fQ[n_] := IntegerQ[ Binomial[2n, n]/(n(n + 1)/2)] && !IntegerQ[ Binomial[2n, n]/n]; Select[ Range@8719, fQ@# &] %Y A120622 Cf. A000108, A000217, A014847, A120623. %K A120622 nonn %O A120622 1,1 %A A120622 _Robert G. Wilson v_, Jun 19 2006 %E A120622 Better description from _Joel B. Lewis_, Nov 15 2006