A192916 Constant term in the reduction by (x^2 -> x+1) of the polynomial C(n)*x^n, where C=A022095.

1, 0, 6, 11, 34, 84, 225, 584, 1534, 4011, 10506, 27500, 72001, 188496, 493494, 1291979, 3382450, 8855364, 23183649, 60695576, 158903086, 416013675, 1089137946, 2851400156, 7465062529, 19543787424, 51166299750, 133955111819, 350699035714, 918141995316

Offset: 0

Author

Clark Kimberling, Jul 12 2011

Keywords

• nonn
• easy

Comments

See A192872.

Links

• Colin Barker, Table of n, a(n) for n = 0..1000
• Index entries for linear recurrences with constant coefficients, signature (2,2,-1).

Crossrefs

Cf. A000045, A192232, A192744, A192872, A192917.

Programs

GAP

F:=Fibonacci;; List([0..30], n-> F(2*n) +2*F(n)*F(n-1) +(-1)^n); # G. C. Greubel, Jul 28 2019

Magma

F:=Fibonacci; [F(2*n) +2*F(n)*F(n-1) +(-1)^n: n in [0..30]]; // G. C. Greubel, Jul 28 2019

Mathematica

(* First program *)
q = x^2; s = x + 1; z = 28;
p[0, x_]:= 1; p[1, x_]:= 5 x;
p[n_, x_]:= p[n-1, x]*x + p[n-2, x]*x^2;
Table[Expand[p[n, x]], {n, 0, 7}]
reduce[{p1_, q_, s_, x_}]:= FixedPoint[(s PolynomialQuotient @@ #1 + PolynomialRemainder @@ #1 &)[{#1, q, x}] &, p1]
t = Table[reduce[{p[n, x], q, s, x}], {n, 0, z}];
u1 = Table[Coefficient[Part[t, n], x, 0], {n, 1, z}] (* A192914 *)
u2 = Table[Coefficient[Part[t, n], x, 1], {n, 1, z}] (* see A192878 *)
(* Second program *)
With[{F=Fibonacci}, Table[F[2*n] +2*F[n]*F[n-1] +(-1)^n, {n,0,30}]] (* G. C. Greubel, Jul 28 2019 *)

PARI

a(n) = round((2^(-n)*(7*(-2)^n+(3+sqrt(5))^n*(-1+2*sqrt(5))-(3-sqrt(5))^n*(1+2*sqrt(5))))/5) \\ Colin Barker, Oct 01 2016

PARI

Vec((1+4*x^2-2*x)/((1+x)*(1-3*x+x^2)) + O(x^30)) \\ Colin Barker, Oct 01 2016

PARI

vector(30, n, n--; f=fibonacci; f(2*n) +2*f(n)*f(n-1) +(-1)^n) \\ G. C. Greubel, Jul 28 2019

Sage

f=fibonacci; [f(2*n) +2*f(n)*f(n-1) +(-1)^n for n in (0..30)] # G. C. Greubel, Jul 28 2019

Formula

a(n) = 2*a(n-1) + 2*a(n-2) - a(n-3).

G.f.: (1 -2*x +4*x^2)/((1+x)*(1-3*x+x^2)). - R. J. Mathar, May 08 2014

a(n) + a(n+1) = A054492(n). - R. J. Mathar, May 07 2014

a(n) = (2^(-n)*(7*(-2)^n+(3+sqrt(5))^n*(-1+2*sqrt(5))-(3-sqrt(5))^n*(1+2*sqrt(5))))/5. - Colin Barker, Oct 01 2016

a(n) = Fibonacci(2*n) + 2*Fibonacci(n)*Fibonacci(n-1) + (-1)^n. - G. C. Greubel, Jul 28 2019