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 A140733 #4 Mar 03 2013 13:49:19 %S A140733 1,1,1,1,1,2,3,3,3,1,3,6,10,15,15,15,1,4,10,22,43,70,105,105,105,1,5, %T A140733 15,40,95,201,390,630,945,945,945,1,6,21,65,180,456,1066,2226,4305, %U A140733 6930,10395,10395,10395,1,7,28,98,308,896,2422,6028,13993,29043,56070,90090 %N A140733 Triangle read by rows, X^n * [1,0,0,0,...]; where X = a tridiagonal matrix with (1,1,1,...) in the main and subdiagonals and (1,2,3,...) in the subsubdiagonal. %C A140733 Rightmost terms of each row form A001147: (1, 1, 3, 15, 105, 945,...). %e A140733 First few rows of the triangle are: %e A140733 1; %e A140733 1, 1, 1; %e A140733 1, 2, 3, 3, 3; %e A140733 1, 3, 6, 10, 15, 15, 15; %e A140733 1, 4, 10, 22, 43, 70, 105, 105, 105; %e A140733 1, 5, 15, 40, 95, 201, 390, 630, 945, 945, 945; %e A140733 1, 6, 21, 65, 180, 456, 1066, 2226, 4305, 6930, 10395, 10395, 10395; %e A140733 ... %Y A140733 Cf. A140734, A140735, A001147. %K A140733 nonn,tabl %O A140733 1,6 %A A140733 _Gary W. Adamson_ & _Roger L. Bagula_, May 25 2008