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 A104028 #3 Mar 30 2012 18:36:45
%S A104028 1,-3,12,-73,675,-9048,166901,-4058703,125837748,-4845013765,
%T A104028 226796981895,-12684595018992,835391818484873,-63990023222817531,
%U A104028 5640684058036591260,-566948619030797914657,64452061572236327204235,-8228252550026752605862344
%N A104028 Column 1 of triangle A104027, which is the matrix inverse of the triangle A056241 of even-indexed trinomial coefficients.
%C A104028 Column 0 of triangle A104027 forms signed Hammersley's polynomial p_n(1) (A006846).
%o A104028 (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))))^-1)[n+2,2])}
%Y A104028 Cf. A104027, A006846.
%K A104028 sign
%O A104028 0,2
%A A104028 _Paul D. Hanna_, Feb 26 2005