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A192468
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Constant term of the reduction by x^2->x+3 of the polynomial p(n,x)=1+x^n+x^(2n).
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3
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4, 16, 61, 304, 1546, 8107, 42748, 226240, 1198645, 6353944, 33688474, 178631251, 947215924, 5022815920, 26634734125, 141237718720, 748951245034, 3971518837243, 21060069709228, 111676816254688, 592197081386533, 3140288211876136
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OFFSET
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1,1
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COMMENTS
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For an introduction to reductions of polynomials by substitutions such as x^2->x+3, see A192232.
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LINKS
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FORMULA
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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]
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EXAMPLE
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The first four polynomials p(n,x) and their reductions are as follows:
p(1,x)=1+x+x^2 -> 4+2x
p(2,x)=1+x^2+x^4 -> 16+8x
p(3,x)=1+x^3+x^6 -> 61+44x
p(4,x)=1+x^4+x^8 -> 304+224x.
From these, read
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MATHEMATICA
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Remove["Global`*"];
q[x_] := x + 3; p[n_, x_] := 1 + x^n + x^(2 n);
Table[Simplify[p[n, x]], {n, 1, 5}]
reductionRules = {x^y_?EvenQ -> q[x]^(y/2),
x^y_?OddQ -> x q[x]^((y - 1)/2)};
t = Table[FixedPoint[Expand[#1 /. reductionRules] &, p[n, x]], {n, 1, 30}]
Table[Coefficient[Part[t, n], x, 0], {n, 1, 30}]
Table[Coefficient[Part[t, n], x, 1], {n, 1, 30}]
Table[Coefficient[Part[t, n]/2, x, 1], {n, 1, 30}]
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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