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 A105619 #5 Jun 13 2017 01:36:27 %S A105619 1,-2,1,-2,-4,1,-10,-2,-6,1,-74,-10,-2,-8,1,-706,-74,-10,-2,-10,1, %T A105619 -8162,-706,-74,-10,-2,-12,1,-110410,-8162,-706,-74,-10,-2,-14,1, %U A105619 -1708394,-110410,-8162,-706,-74,-10,-2,-16,1,-29752066,-1708394,-110410,-8162,-706,-74,-10,-2,-18,1 %N A105619 Matrix inverse of triangle A105615. %C A105619 Except for the initial few terms, all columns are equal to negative A000698 (related to double factorials). %e A105619 Triangle begins: %e A105619 1; %e A105619 -2,1; %e A105619 -2,-4,1; %e A105619 -10,-2,-6,1; %e A105619 -74,-10,-2,-8,1; %e A105619 -706,-74,-10,-2,-10,1; %e A105619 -8162,-706,-74,-10,-2,-12,1; %e A105619 -110410,-8162,-706,-74,-10,-2,-14,1; %e A105619 -1708394,-110410,-8162,-706,-74,-10,-2,-16,1; ... %o A105619 (PARI) T(n,k)=if(n<k || k<0,0, matrix(n+1,n+1,m,j,if(m>=j,if(m==j,1,if(m==j+1,-2*j, polcoeff(1/sum(i=0,m-j,(2*i)!/i!/2^i*x^i)+O(x^m),m-j)))))[n+1,k+1]) %Y A105619 Cf. A105615, A000698, A105620 (matrix square-root). %K A105619 sign,tabl %O A105619 0,2 %A A105619 _Paul D. Hanna_, Apr 16 2005