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 A257641 #7 Nov 19 2015 16:38:59 %S A257641 1,1,3,9,30,102,352,1240,4443,16112,58900,216727,801880,2982327, %T A257641 11147622,41854916,157805863,597307573,2268487476,8639848112, %U A257641 32999949539,126498330700,485441076004,1865211479514,7176111235446,27644828367182,106633724636570 %N A257641 Central terms of triangle A103284. %C A257641 a(n) = A103284(2*n,n). %H A257641 Reinhard Zumkeller, <a href="/A257641/b257641.txt">Table of n, a(n) for n = 0..1000</a> %o A257641 (Haskell) %o A257641 a257641 n = a103284 (2 * n) n %Y A257641 Cf. A103284, A103285, A000984. %K A257641 nonn %O A257641 0,3 %A A257641 _Reinhard Zumkeller_, Nov 19 2015