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 A163200 Sum of the cubes of the first n odd-indexed Fibonacci numbers. 6
 0, 1, 9, 134, 2331, 41635, 746604, 13395941, 240376941, 4313380114, 77400441855, 1388894512391, 24922700621784, 447219716262409, 8025032191009041, 144003359719040030, 2584035442744223139, 46368634609657371691, 832051387531037141316, 14930556340948876798829 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Natural bilateral extension (brackets mark index 0): ..., -41635, -2331, -134, -9, -1, [0], 1, 9, 134, 2331, 41635, ... This is (-A163200)-reversed followed by A163200, without repeating the 0. That is, a(-n) = -a(n). Thus a(n) is an odd function of n. LINKS G. C. Greubel, Table of n, a(n) for n = 0..500 K. Subba Rao, Some properties of Fibonacci numbers, Amer. Math. Monthly, 60(10):680-684, Dec. 1953. See page 682. Index entries for linear recurrences with constant coefficients, signature (21,-56,21,-1). FORMULA Let F(n) be the Fibonacci number A000045(n) and let L(n) be the Lucas number A000032(n). a(n) = Sum_{k=1..n} F(2k-1)^3. a(n) = (1/20)*(F(6*n) + 12*F(2*n)). a(n) = (1/4)*(F(2n)^3 + 3*F(2n)). (K. Subba Rao) a(n) = (1/20)*F(2n)*(L(4n) + 13). a(n) = (1/4)*F(2n)*(F(2n)^2 + 3). a(n) - 21*a(n-1) + 56*a(n-2) - 21*a(n-3) + a(n-4) = 0. G.f.: (x - 12*x^2 + x^3)/(1 - 21*x + 56*x^2 - 21*x^3 + x^4) = x*(1 - 12*x + x^2)/((1 - 3*x + x^2 )*(1 - 18*x + x^2)). MATHEMATICA a[n_Integer] := If[ n >= 0, Sum[ Fibonacci[2k-1]^3, {k, 1, n} ], -Sum[ Fibonacci[-2k+1]^3, {k, 1, -n} ] ] LinearRecurrence[{21, -56, 21, -1}, {0, 1, 9, 134}, 50] (* or *) Table[(1/20)*(Fibonacci[6*n] + 12*fibonacci[2*n]), {n, 0, 25}] (* G. C. Greubel, Dec 09 2016 *) PROG (PARI) concat([0], Vec(x*(1 - 12*x + x^2)/((1 - 3*x + x^2 )*(1 - 18*x + x^2)) + O(x^50))) \\ G. C. Greubel, Dec 09 2016 (MAGMA) [(1/4)*Fibonacci(2*n)*(Fibonacci(2*n)^2+3): n in [0..20]]; // Vincenzo Librandi, Dec 10 2016 CROSSREFS Cf. A005968, A163198, A163201, A163202. Sequence in context: A268654 A112426 A213688 * A279975 A296171 A167893 Adjacent sequences:  A163197 A163198 A163199 * A163201 A163202 A163203 KEYWORD nonn,easy AUTHOR Stuart Clary, Jul 24 2009 STATUS approved

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Last modified December 5 16:12 EST 2019. Contains 329753 sequences. (Running on oeis4.)