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A152119 a(n) = prod(k=1..(n-1)/2, 5 + 4*cos(k*Pi/n)^2 ). 1
1, 1, 1, 6, 7, 41, 48, 281, 329, 1926, 2255, 13201, 15456, 90481, 105937, 620166, 726103, 4250681, 4976784, 29134601, 34111385, 199691526, 233802911, 1368706081, 1602508992, 9381251041, 10983760033, 64300051206, 75283811239 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

LINKS

Table of n, a(n) for n=0..28.

P. Barry, Symmetric Third-Order Recurring Sequences, Chebyshev Polynomials, and Riordan Arrays, JIS 12 (2009) 09.8.6

Index entries for linear recurrences with constant coefficients, signature (0,7,0,-1).

FORMULA

a(n) = prod(k=1..(n-1)/2, 5 + 4*cos(k*Pi/n)^2 ).

a(n) = 7*a(n-2) -a(n-4). G.f.: (x^4 - x^3 - 6*x^2 + x + 1)/((x^2 - 3*x + 1)*(x^2 + 3*x + 1)). [Joerg Arndt, Jan 24 2013]

MATHEMATICA

a = Table[Product[5 + 4*Cos[k*Pi/n]^2, {k, 1, (n - 1)/2}], {n, 0, 10}]; FullSimplify[ExpandAll[a]]

Denominator[NestList[(5/(5+#))&, 0, 60]] (* Vladimir Joseph Stephan Orlovsky, Apr 13 2010 *)

CROSSREFS

Cf. A004187 (bisection), A049685 (bisection).

Sequence in context: A294728 A219212 A301904 * A041080 A042091 A047181

Adjacent sequences:  A152116 A152117 A152118 * A152120 A152121 A152122

KEYWORD

nonn,easy

AUTHOR

Roger L. Bagula and Gary W. Adamson, Nov 24 2008

STATUS

approved

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Last modified March 19 13:29 EDT 2019. Contains 321330 sequences. (Running on oeis4.)