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 A306603 a(n) = (2 cos(Pi/15))^n + (2 cos(7 Pi/15))^n + (2 cos(11 Pi/15))^n + (2 cos(13 Pi/15))^n. 3
 4, -1, 9, -1, 29, 4, 99, 34, 349, 179, 1254, 824, 4559, 3574, 16704, 15004, 61549, 61709, 227799, 250229, 846254, 1004149, 3153984, 3997399, 11788879, 15812504, 44178624, 62229509, 165946124, 243873904, 624650004, 952400599, 2355748909, 3708579599 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS a(n) is obtained from the Girard-Waring formula for the sum of powers of N = 4 indeterminates (see A324602), with the elementary symmetric functions e_1 = -1, e_2 = -4, e_3 = -4 and e_4 = 1. The arguments are e_j(x_1, x_2, x_3, x_4), for j = 1..4, with the zeros {x_i}_{i=1..4} of the minimal polynomial of 2*cos(Pi/15) (see A187360, for n = 15), appearing to the power n in the formula given above. - Wolfdieter Lang, May 08 2019 LINKS Index entries for linear recurrences with constant coefficients, signature (-1,4,4,-1). FORMULA G.f.: (4*x^3+8*x^2-3*x-4)/(-x^4+4*x^3+4*x^2-x-1). - Alois P. Heinz, Feb 27 2019 a(n) = -a(n-1) + 4*a(n-2) + 4*a(n-3) -a(n-4). - Greg Dresden, Feb 27 2019 MATHEMATICA Table[Sum[(2.0 Cos[k Pi/15])^n, {k, {1, 7, 11, 13}}] // Round, {n, 1, 30}] CROSSREFS Cf. A019887 (cos(Pi/15)), A019815 (cos(7*Pi/15)), A019851 (cos(11*Pi/15)), A019875 (cos(13*Pi/15)), A187360, A324602. Sequence in context: A091419 A326582 A276171 * A181859 A218972 A331151 Adjacent sequences:  A306600 A306601 A306602 * A306604 A306605 A306606 KEYWORD sign,easy AUTHOR Greg Dresden, Feb 27 2019 STATUS approved

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Last modified August 2 11:06 EDT 2021. Contains 346422 sequences. (Running on oeis4.)