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Constant term of the reduction of n-th polynomial at A157751 by x^2->x+1.
3

%I #7 Nov 13 2012 12:46:02

%S 1,2,5,13,34,91,247,680,1893,5319,15056,42867,122605,351898,1012729,

%T 2920521,8435362,24392655,70599403,204472264

%N Constant term of the reduction of n-th polynomial at A157751 by x^2->x+1.

%C For an introduction to reductions of polynomials by substitutions such as x^2->x+1, see A192232.

%F Empirical G.f.: x*(x+1)*(x^2-3*x+1)/(x^4+6*x^3+x^2-4*x+1). [_Colin Barker_, Nov 13 2012]

%e The first five polynomials at A157751 and their reductions are as follows:

%e p0(x)=1 -> 1

%e p1(x)=2+x -> 2+x

%e p2(x)=4+2x+x^2 -> 5+3x

%e p3(x)=8+4x+4x^2+x^3 -> 13+10x

%e p4(x)=16+8x+12x^2+4x^3+x^4 -> 34+31x.

%e From these, we read

%e A192313=(1,2,5,13,34,...) and A192314=(0,1,3,19,31,...)

%t q[x_] := x + 1;

%t p[0, x_] := 1;

%t p[n_, x_] := (x + 1)*p[n - 1, x] + p[n - 1, -x] /; n > 0 (* A157751 *)

%t Table[Simplify[p[n, x]], {n, 0, 5}]

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

%t t = Table[Last[Most[FixedPointList[Expand[#1 /. reductionRules] &, p[n, x]]]], {n, 0, 20}]

%t Table[Coefficient[Part[t, n], x, 0], {n, 1, 20}]

%t (* A192313 *)

%t Table[Coefficient[Part[t, n], x, 1], {n, 1, 20}]

%t (* A192337 *)

%Y Cf. A192232, A192337.

%K nonn

%O 1,2

%A _Clark Kimberling_, Jun 28 2011