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 A104031 #5 Jan 25 2013 19:01:52
%S A104031 1,-5,32,-299,4015,-74080,1801537,-55855829,2150565968,-100668835739,
%T A104031 5630336915071,-370807060847872,28403381397111649,
%U A104031 -2503741873703550533,251652633457563092096,-28608467296650576313259,3652291148549164761101551,-520296573821474451201241696
%N A104031 Column 1 of triangle A104030, which is the matrix inverse of the triangle of pairwise sums of trinomial coefficients.
%C A104031 Column 0 of triangle A104030 forms signed Hammersley's polynomial p_n(1) (A006846), offset 1.
%o A104031 (PARI) {a(n)=if(n<0,0,((matrix(n+2,n+2,m,j,if(m>=j, polcoeff((1+x+x^2)^(m-1)+O(x^(2*j)),2*j-2)+ polcoeff((1+x+x^2)^(m-1)+O(x^(2*j)),2*j-1))))^-1)[n+2,2])}
%Y A104031 Cf. A104030.
%K A104031 sign
%O A104031 0,2
%A A104031 _Paul D. Hanna_, Feb 26 2005