OFFSET
0,2
COMMENTS
a(n+1)/a(n) tends to (1 + sqrt(11) + sqrt(2*(4+sqrt(11))))/2 = 4.070983928708143809... - Vaclav Kotesovec, Nov 30 2012
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..300
FORMULA
G.f.: 1 + 2*(1-x)*x*(1+x)/(1-2*x-8*x^2-2*x^3+x^4). - Vaclav Kotesovec, Nov 30 2012
MATHEMATICA
With[{m = 6, q = 4}, Table[2^n*Round[Product[1 + m*Cos[k*Pi/n]^2 + q*Cos[k*Pi/n]^4, {k, 1, (n - 1)/2}]], {n, 0, 30}]] (* modified by G. C. Greubel, May 15 2019 *)
CoefficientList[Series[1+2*(1-x)*x*(1+x)/(1-2*x-8*x^2-2*x^3+x^4), {x, 0, 20}], x] (* Vaclav Kotesovec, Nov 30 2012 *)
PROG
(PARI) my(x='x+O('x^30)); Vec(1+2*(1-x)*x*(1+x)/(1-2*x-8*x^2-2*x^3+x^4)) \\ G. C. Greubel, May 15 2019
(Magma) R<x>:=PowerSeriesRing(Integers(), 30); Coefficients(R!( 1+2*(1-x)*x*(1+x)/(1-2*x-8*x^2-2*x^3+x^4) )); // G. C. Greubel, May 15 2019
(Sage) (1+2*(1-x)*x*(1+x)/(1-2*x-8*x^2-2*x^3+x^4)).series(x, 30).coefficients(x, sparse=False) # G. C. Greubel, May 15 2019
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Roger L. Bagula, Nov 24 2008
STATUS
approved