OFFSET
0,4
FORMULA
Conjecture: a(2n) = A108196(n-1), n>=2. a(n) = (-1)^(n+1)*A000045(n) *A101675(n-1), n>0. G.f.: 1 -x*(x-1)*(x^2-x+1)*(1+x)^3 / ( (x^4-x^3+2*x^2+x+1)*(x^4+x^3+2*x^2-x+1) ). - R. J. Mathar, Mar 08 2011
MATHEMATICA
f[n_] = Product[(1 + 4*Cos[k*Pi/n]^2)*(1 - 4*Sin[k*Pi/n]^2), {k, 1, Floor[(n - 1)/2]}]; Table[N[f[n]], {n, 0, 30}]; Round[%]
PROG
(PARI) a(n) = round(prod(k=1, floor((n-1)/2), (1+4*cos(k*Pi/n)^2)*(1-4*sin(k*Pi/n)^2))) \\ Colin Barker, Apr 11 2014
CROSSREFS
KEYWORD
sign
AUTHOR
Roger L. Bagula and Gary W. Adamson, Nov 28 2008
EXTENSIONS
More terms from Colin Barker, Apr 11 2014
STATUS
approved