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 A155050 #5 Feb 26 2014 09:54:35
%S A155050 1,1,1,1,1,1,1,1,1,1,1,1,2,1,1,1,1,2,2,1,1,1,1,2,5,2,1,1,1,1,2,5,5,2,
%T A155050 1,1,1,1,2,5,14,5,2,1,1,1,1,2,5,14,14,5,2,1,1,1,1,2,5,14,42,14,5,2,1,
%U A155050 1,1,1,2,5,14,42,42,14,5,2,1,1,1,1,2,5,14,42,132,42,14,5,2,1,1
%N A155050 A symmetric Catalan based triangle.
%C A155050 Central coefficients are A000108. Row sums are A155051.
%C A155050 Image under Riordan array ((1+x)/(1-x),x)^{-1} is A155052.
%F A155050 Number triangle T(n,k)=sum{j=0..n, [j<=k]*[j<=n-k]*(ct(j+1)-ct(j))} where ct(n):=if(n=0,0,A000108(n-1)).
%F A155050 T(n,k) = A000108(min(k, n-k)). - _Philippe Deléham_, Feb 26 2014
%e A155050 Triangle begins
%e A155050 1,
%e A155050 1, 1,
%e A155050 1, 1, 1,
%e A155050 1, 1, 1, 1,
%e A155050 1, 1, 2, 1, 1,
%e A155050 1, 1, 2, 2, 1, 1,
%e A155050 1, 1, 2, 5, 2, 1, 1,
%e A155050 1, 1, 2, 5, 5, 2, 1, 1,
%e A155050 1, 1, 2, 5, 14, 5, 2, 1, 1,
%e A155050 1, 1, 2, 5, 14, 14, 5, 2, 1, 1,
%e A155050 1, 1, 2, 5, 14, 42, 14, 5, 2, 1, 1
%Y A155050 Cf. A000108, A155051
%K A155050 easy,nonn,tabl
%O A155050 0,13
%A A155050 _Paul Barry_, Jan 19 2009