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 A209569 #5 Mar 30 2012 18:58:15 %S A209569 1,1,1,2,3,1,3,6,5,1,4,11,14,7,1,5,18,31,26,9,1,6,27,60,71,42,11,1,7, %T A209569 38,105,162,139,62,13,1,8,51,170,327,372,243,86,15,1,9,66,259,602,861, %U A209569 754,391,114,17,1,10,83,376,1031,1790,1987,1388,591,146,19,1 %N A209569 Triangle of coefficients of polynomials u(n,x) jointly generated with A209570; see the Formula section. %C A209569 For n>1, row n begins with n and ends with 2. %C A209569 Alternating row sums: 1,0,0,1,1,0,0,1,1,0,0,1,1,... %C A209569 For a discussion and guide to related arrays, see A208510. %F A209569 u(n,x)=x*u(n-1,x)+v(n-1,x), %F A209569 v(n,x)=2x*u(n-1,x)+v(n-1,x)+1, %F A209569 where u(1,x)=1, v(1,x)=1. %e A209569 First five rows: %e A209569 1 %e A209569 1...1 %e A209569 2...3....1 %e A209569 3...6....5....1 %e A209569 4...11...14...7...1 %e A209569 First three polynomials v(n,x): 1, 1 + x, 2 + 3x + x^2. %t A209569 u[1, x_] := 1; v[1, x_] := 1; z = 16; %t A209569 u[n_, x_] := x*u[n - 1, x] + v[n - 1, x]; %t A209569 v[n_, x_] := 2 x*u[n - 1, x] + v[n - 1, x] + 1; %t A209569 Table[Expand[u[n, x]], {n, 1, z/2}] %t A209569 Table[Expand[v[n, x]], {n, 1, z/2}] %t A209569 cu = Table[CoefficientList[u[n, x], x], {n, 1, z}]; %t A209569 TableForm[cu] %t A209569 Flatten[%] (* A209569 *) %t A209569 Table[Expand[v[n, x]], {n, 1, z}] %t A209569 cv = Table[CoefficientList[v[n, x], x], {n, 1, z}]; %t A209569 TableForm[cv] %t A209569 Flatten[%] (* A209570 *) %Y A209569 Cf. A209570, A208510. %K A209569 nonn,tabl %O A209569 1,4 %A A209569 _Clark Kimberling_, Mar 10 2012