A192468 - OEIS

%I #7 Nov 12 2012 09:55:04

%S 4,16,61,304,1546,8107,42748,226240,1198645,6353944,33688474,

%T 178631251,947215924,5022815920,26634734125,141237718720,748951245034,

%U 3971518837243,21060069709228,111676816254688,592197081386533,3140288211876136

%N Constant term of the reduction by x^2->x+3 of the polynomial p(n,x)=1+x^n+x^(2n).

%C For an introduction to reductions of polynomials by substitutions such as x^2->x+3, see A192232.

%F Empirical G.f.: -x*(81*x^4-87*x^3-x^2+20*x-4)/((x-1)*(3*x^2+x-1)*(9*x^2-7*x+1)). [_Colin Barker_, Nov 12 2012]

%e The first four polynomials p(n,x) and their reductions are as follows:

%e p(1,x)=1+x+x^2 -> 4+2x

%e p(2,x)=1+x^2+x^4 -> 16+8x

%e p(3,x)=1+x^3+x^6 -> 61+44x

%e p(4,x)=1+x^4+x^8 -> 304+224x.

%e From these, read

%e A192468=(4,16,61,304,...) and A192469=(2,8,44,224,...)

%t Remove["Global`*"];

%t q[x_] := x + 3; p[n_, x_] := 1 + x^n + x^(2 n);

%t Table[Simplify[p[n, x]], {n, 1, 5}]

%t reductionRules = {x^y_?EvenQ -> q[x]^(y/2),

%t    x^y_?OddQ -> x q[x]^((y - 1)/2)};

%t t = Table[FixedPoint[Expand[#1 /. reductionRules] &, p[n, x]], {n, 1, 30}]

%t Table[Coefficient[Part[t, n], x, 0], {n, 1, 30}]

%t (* A192468 *)

%t Table[Coefficient[Part[t, n], x, 1], {n, 1, 30}]

%t (* A192469 *)

%t Table[Coefficient[Part[t, n]/2, x, 1], {n, 1, 30}]

%t (* A192470 *)

%Y Cf. A192232, A192468, A192464, A192465.

%K nonn

%O 1,1

%A _Clark Kimberling_, Jul 01 2011