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A152190
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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]}].
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0
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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,4
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COMMENTS
| It appears that Limit[Sqrt[a[n+2]/a[n]],n->Infinity]=1+(Sqrt[5]+1)/2.
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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[%]
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CROSSREFS
| Sequence in context: A087098 A109315 A024875 * A079322 A167304 A191966
Adjacent sequences: A152187 A152188 A152189 * A152191 A152192 A152193
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KEYWORD
| nonn
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AUTHOR
| Roger L. Bagula (rlbagulatftn(AT)yahoo.com), Nov 28 2008
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