A192467 -id:A192467 - cp's OEIS frontend

A192465 Constant term of the reduction by x^2->x+2 of the polynomial p(n,x)=1+x^n+x^(2n).

3, 9, 25, 93, 353, 1389, 5505, 21933, 87553, 349869, 1398785, 5593773, 22372353, 89483949, 357924865, 1431677613, 5726666753, 22906579629, 91626143745, 366504225453, 1466016202753, 5864063412909, 23456250855425, 93824997829293

Offset: 1

Clark Kimberling, Jul 01 2011

nonn

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

			The first four polynomials p(n,x) and their reductions are as follows:
p(1,x)=1+x+x^2 -> 3+2x
p(2,x)=1+x^2+x^4 -> 9+6x
p(3,x)=1+x^3+x^6 -> 25+24x
p(4,x)=1+x^4+x^8 -> 93+90x.
From these, read
A192465=(3,9,25,93,...) and A192466=(2,6,24,90,...)

Cf. A192232, A192466, A192464.

Remove["Global`*"];
q[x_] := x + 2; 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}]
(* A192465 *)
Table[Coefficient[Part[t, n], x, 1], {n, 1, 30}]
(* A192466 *)
Table[Coefficient[Part[t, n]/2, x, 1], {n, 1, 30}]
(* A192467 *)

Empirical G.f.: -x*(3*x-1)*(8*x^2-3)/((x-1)*(x+1)*(2*x-1)*(4*x-1)). [Colin Barker, Nov 12 2012]

A192466 Coefficient of x in the reduction by x^2->x+2 of the polynomial p(n,x)=1+x^n+x^(2n).

Original entry on oeis.org

2, 6, 24, 90, 352, 1386, 5504, 21930, 87552, 349866, 1398784, 5593770, 22372352, 89483946, 357924864, 1431677610, 5726666752, 22906579626, 91626143744, 366504225450, 1466016202752, 5864063412906, 23456250855424, 93824997829290

Offset: 1

Clark Kimberling, Jul 01 2011

nonn

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

			The first four polynomials p(n,x) and their reductions are as follows:
p(1,x)=1+x+x^2 -> 3+2x
p(2,x)=1+x^2+x^4 -> 9+6x
p(3,x)=1+x^3+x^6 -> 25+24x
p(4,x)=1+x^4+x^8 -> 93+90x.
From these, read
A192465=(3,9,25,93,...) and A192466=(2,6,24,90,...)

Yuanan Diao, Michael Finney, and Dawn Ray, The number of oriented rational links with a given deficiency number, arXiv:2007.02819 [math.GT], 2020. See p. 16.

Cf. A192232, A192465, A192467.

Mathematica
```
(See A192465.)
```

Empirical G.f.: -2*x*(x^2 - 3*x + 1) / ((x - 1)*(x + 1)*(2*x - 1)*(4*x - 1)). - Colin Barker, Nov 12 2012
Conjectures from Colin Barker, Feb 14 2017: (Start)
a(n) = (-1 - (-1)^n + 2^n + 4^n) / 3.
a(n) = 6*a(n-1) - 7*a(n-2) - 6*a(n-3) + 8*a(n-4) for n>4.
(End)

cp's OEIS Frontend

A192465 Constant term of the reduction by x^2->x+2 of the polynomial p(n,x)=1+x^n+x^(2n).

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