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 A210213 #4 Mar 30 2012 18:58:16 %S A210213 1,2,1,4,3,1,7,9,4,1,12,21,16,5,1,20,46,46,25,6,1,33,94,121,85,36,7,1, %T A210213 54,185,289,260,141,49,8,1,88,353,653,708,491,217,64,9,1,143,659,1409, %U A210213 1800,1499,847,316,81,10,1,232,1209,2939,4320,4229,2863,1366 %N A210213 Triangle of coefficients of polynomials u(n,x) jointly generated with A210214; see the Formula section. %C A210213 Row sums: even-indexed Fibonacci numbers %C A210213 For a discussion and guide to related arrays, see A208510. %F A210213 u(n,x)=x*u(n-1,x)+v(n-1,x)+1, %F A210213 v(n,x)=u(n-1,x)+(x+1)*v(n-1,x)+1, %F A210213 where u(1,x)=1, v(1,x)=1. %e A210213 First five rows: %e A210213 1 %e A210213 2....1 %e A210213 4....3....1 %e A210213 7....9....4....1 %e A210213 12...21...16...5...1 %e A210213 First three polynomials u(n,x): 1, 2 + x, 4 + 3x + x^2. %t A210213 u[1, x_] := 1; v[1, x_] := 1; z = 16; %t A210213 u[n_, x_] := x*u[n - 1, x] + v[n - 1, x] + 1; %t A210213 v[n_, x_] := u[n - 1, x] + (x + 1)*v[n - 1, x] + 1; %t A210213 Table[Expand[u[n, x]], {n, 1, z/2}] %t A210213 Table[Expand[v[n, x]], {n, 1, z/2}] %t A210213 cu = Table[CoefficientList[u[n, x], x], {n, 1, z}]; %t A210213 TableForm[cu] %t A210213 Flatten[%] (* A210213 *) %t A210213 Table[Expand[v[n, x]], {n, 1, z}] %t A210213 cv = Table[CoefficientList[v[n, x], x], {n, 1, z}]; %t A210213 TableForm[cv] %t A210213 Flatten[%] (* A210214 *) %Y A210213 Cf. A210214, A208510. %K A210213 nonn,tabl %O A210213 1,2 %A A210213 _Clark Kimberling_, Mar 19 2012