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 A133366 #12 Jan 25 2020 02:29:47
%S A133366 1,3,1,12,7,1,57,43,11,1,300,262,90,15,1,1686,1618,667,153,19,1,9912,
%T A133366 10159,4745,1336,232,23,1,60213,64783,33147,10785,2333,327,27,1,
%U A133366 374988,418786,229726,83286,21098,3722,438,31,1
%N A133366 Triangle T(n,k)read by rows given by [3,1,3,1,3,1,3,1,3,1,3,1,...] DELTA [1,0,0,0,0,0,0,0,...] where DELTA is the operator defined in A084938.
%C A133366 A121576*A007318 as infinite lower triangular matrices.
%F A133366 T(0,0)=1; T(n,k) = 0 if k < 0 or if k > n; T(n,0) = 3*T(n-1,0) + 3*T(n-1,1); T(n,k) = T(n-1,k-1) + 4*T(n-1,k) + 3*T(n-1,k+1) for k >= 1.
%F A133366 Sum_{k>=0} T(m,k)*T(n,k)*3^k = T(m+n,0)= A047891(m+n+1). - _Philippe Deléham_, Jan 24 2010
%e A133366 Triangle begins:
%e A133366 1;
%e A133366 3, 1;
%e A133366 12, 7, 1;
%e A133366 57, 43, 11, 1;
%e A133366 300, 262, 90, 15, 1;
%e A133366 1686, 1618, 667, 153, 19, 1;
%e A133366 9912, 10159, 4745, 1336, 232, 23, 1;
%e A133366 60213, 64783, 33147, 10785, 2333, 327, 27, 1;
%e A133366 374988, 418786, 229786, 83286, 21098, 3722, 438, 31, 1; ...
%Y A133366 Cf. A047891, A000012, A004767.
%Y A133366 Cf. A007318, A121576.
%K A133366 nonn,tabl
%O A133366 0,2
%A A133366 _Philippe Deléham_, Oct 27 2007