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 A168591 #2 Mar 30 2012 18:37:20 %S A168591 1,3,19,831,281907,764206503,16955359883149,3120135986465328015, %T A168591 4819828380706011142058787,63004580363300194268932114354503, %U A168591 7017256966823394610075464951176481843849 %N A168591 a(n) = sum of the n-th power of the trinomial coefficients in row n of triangle A027907. %F A168591 Ignoring initial term, equals the logarithmic derivative of A168590. %o A168591 (PARI) a(n)=sum(k=0,2*n,polcoeff((1+x+x^2)^n,k)^n) %Y A168591 Cf. A168590, A027907. %K A168591 nonn %O A168591 0,2 %A A168591 _Paul D. Hanna_, Dec 01 2009