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 A200613 #13 Sep 16 2012 02:50:25
%S A200613 1,3,11,44,183,774,3294,14034,59711,253430,1072506,4525168,19036726,
%T A200613 79861404,334155036,1394789214,5808981711,24143440374,100156051746,
%U A200613 414762312504,1714844273586,7079573497524,29187378344676,120180109515204,494264431607718,2030539136846844
%N A200613 Number of quasi-abelian ideals in the affine Lie algebra sl_n^{hat}.
%C A200613 Christian Krattenthaler has shown that a(n)=((n+4)/4)*binomial(2*n,n)-3*2^(2*n-3). This implies that a(n)=A194460(n) - A000531(n-1). The latter fact was first empirically observed by D. S. McNeil. [_Volodymyr Mazorchuk_, Sep 14 2012]
%H A200613 Karin Baur and Volodymyr Mazorchuk, <a href="http://arxiv.org/abs/1108.3659">Combinatorial analogues of ad-nilpotent ideals for untwisted affine Lie algebras</a>, arXiv:1108.3659 [math.RA]
%F A200613 a(n) = ((n+4)/4)*binomial(2*n,n)-3*2^(2*n-3). [_Volodymyr Mazorchuk_, Sep 14 2012]
%o A200613 (PARI) a(n) = ((n+4)/4)*binomial(2*n,n)-3*2^(2*n-3);
%K A200613 nonn
%O A200613 1,2
%A A200613 _N. J. A. Sloane_, Nov 19 2011