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 A249268 #14 Nov 22 2014 03:47:03
%S A249268 1,4,1,-23,-5,1,-320,-86,10,1,4297,1102,-152,-11,1,92020,24187,-3122,
%T A249268 -281,16,1,-1922207,-502151,66133,5659,-389,-17,1,-55746464,-14601740,
%U A249268 1908316,167254,-10784,-584,22,1,1589338993,415992316,-54490040,-4745234,312406,16048,-734,-23,1
%N A249268 Triangle read by rows: T(n,k) is the coefficient A_k in the transformation Sum_{k=0..n} x^k = Sum_{k=0..n} A_k*(x+3*(-1)^k)^k.
%C A249268 Consider the transformation 1 + x + x^2 + x^3 + ... + x^n = A_0*(x+3)^0 + A_1*(x-3)^1 + A_2*(x+3)^2 + A_3*(x-3)^3 + ... + A_n*(x+3*(-1)^n)^n. This sequence gives A_0, ... A_n as the entries in the n-th row of this triangle, starting at n = 0.
%e A249268 Triangle starts:
%e A249268 1;
%e A249268 4, 1;
%e A249268 -23, -5, 1;
%e A249268 -320, -86, 10, 1;
%e A249268 4297, 1102, -152, -11, 1;
%e A249268 92020, 24187, -3122, -281, 16, 1;
%e A249268 -1922207, -502151, 66133, 5659, -389, -17, 1;
%e A249268 -55746464, -14601740, 1908316, 167254, -10784, -584, 22, 1;
%e A249268 1589338993, 415992316, -54490040, -4745234, 312406, 16048, -734, -23, 1;
%e A249268 ...
%o A249268 (PARI) a(n, j, L)=if(j==n, return(1)); if(j!=n, return(1-sum(i=1, n-j, (-L)^i*(-1)^(i*j)*binomial(i+j, i)*a(n, i+j, L))))
%o A249268 for(n=0, 10, for(j=0, n, print1(a(n, j, 3), ", ")))
%Y A249268 Cf. A248975, A248977, A248811.
%K A249268 sign,tabl
%O A249268 0,2
%A A249268 _Derek Orr_, Oct 23 2014