A152190 a(n)=2*Product[(1 + 4*Cos[k*Pi/n]^2)*(1 + 4*Sin[k*Pi/n]^2), {k, 1, Floor[(n - 1)/2]}] - Product[(1 + 4*Sin[k*Pi/n]^2), {k, 1, Floor[(n - 1)/2]}].

1, 1, 1, 12, 15, 99, 120, 725, 861, 5092, 5995, 35223, 41328, 242265, 283881, 1662716, 1947351, 11402203, 13351528, 78166989, 91523685, 535804116, 627341331, 3672559727, 4299936480, 25172370289, 29472399505, 172534703340

Offset

0,4

Comments

It appears that Limit[Sqrt[a[n+2]/a[n]],n->Infinity]=1+(Sqrt[5]+1)/2.

Links

Table of n, a(n) for n=0..27.

Mathematica

f[n_] = 2*Product[(1 + 4*Cos[k*Pi/n]^2)*(1 + 4*Sin[k*Pi/n]^2), {k, 1, Floor[(n - 1)/2]}] - Product[(1 + 4*Sin[k*Pi/n]^2), {k, 1, Floor[(n - 1)/2]}]; Table[N[f[n]], {n, 0, 30}]; Floor[%]

Crossrefs

Sequence in context: A087098 A109315 A024875 * A330367 A079322 A167304

Adjacent sequences: A152187 A152188 A152189 * A152191 A152192 A152193

Keyword

nonn

Author

Roger L. Bagula, Nov 28 2008

Status

approved