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 A048876 a(n) = 4*a(n-1) + a(n-2); a(0)=1, a(1)=7. 10
 1, 7, 29, 123, 521, 2207, 9349, 39603, 167761, 710647, 3010349, 12752043, 54018521, 228826127, 969323029, 4106118243, 17393796001, 73681302247, 312119004989, 1322157322203, 5600748293801, 23725150497407, 100501350283429, 425730551631123, 1803423556807921 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Generalized Pell equation with second term of 7. LINKS T. D. Noe, Table of n, a(n) for n = 0..200 M. Bicknell, A Primer on the Pell Sequence and related sequences, Fibonacci Quarterly, Vol. 13, No. 4, 1975, pp. 345-349. L. Carlitz, R. Scoville and V. E. Hoggatt, Jr., Pellian Representations, Fib. Quart. Vol. 10, No. 5, (1972), pp. 449-488. Tanya Khovanova, Recursive Sequences A. K. Whitford, Binet's Formula Generalized, Fibonacci Quarterly, Vol. 15, No. 1, 1979, pp. 21, 24, 29. Index entries for linear recurrences with constant coefficients, signature (4,1). FORMULA G.f.: (1+3*x)/(1-4*x-x^2). - Philippe Deléham, Nov 03 2008 a(n) = ((1+sqrt(5))*(2+sqrt(5))^n + (1-sqrt(5))*(2-sqrt(5))^n )/2. a(n) = A000032(3*n+1). - Thomas Baruchel, Nov 26 2003 From Gary Detlefs, Mar 06 2011: (Start) a(n) = Fibonacci(3*n+7) mod Fibonacci(3*n+3), n > 0. a(n) = Fibonacci(3*n+3) - Fibonacci(3*n-1). (End) a(n) = A001076(n+1)+3*A001076(n). - R. J. Mathar, Oct 22 2013 a(n) = 5*F(2*n)*F(n+1) - L(n-1)*(-1)^n. - J. M. Bergot, Mar 22 2016 a(n) = Sum_{k=0..n} binomial(n,k)*5^floor((k+1)/2)*2^(n-k). - Tony Foster III, Sep 03 2017 MAPLE with(combinat): a:=n->3*fibonacci(n-1, 4)+fibonacci(n, 4): seq(a(n), n=1..16); # Zerinvary Lajos, Apr 04 2008 MATHEMATICA f[n_] := Block[{s = Sqrt@ 5}, Simplify[((1 + s)(2 + s)^n + (1 - s)(2 - s)^n)/2]]; (* Or *) f[n_] := Fibonacci[3 n + 3] - Fibonacci[3 n - 1]; (* Or *) f[n_] := Mod[ Fibonacci[3n + 7], Fibonacci[3n + 3]]; Array[f, 22, 0] a[n_] := 4a[n - 1] + a[n - 2]; a[0] = 1; a[1] = 7; Array[a, 22, 0] (* Or *) CoefficientList[ Series[(1 + 3x)/(1 - 4x - x^2), {x, 0, 21}], x] (* Robert G. Wilson v *) LinearRecurrence[{4, 1}, {1, 7}, 30] (* Harvey P. Dale, Jun 13 2015 *) PROG (PARI) Vec((1+3*x)/(1-4*x-x^2) + O(x^30)) \\ Altug Alkan, Oct 07 2015 CROSSREFS Cf. A001076, A001077, A015448, A033887. Sequence in context: A066744 A037576 A055427 * A126394 A252832 A074468 Adjacent sequences:  A048873 A048874 A048875 * A048877 A048878 A048879 KEYWORD easy,nonn AUTHOR STATUS approved

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Last modified September 25 18:05 EDT 2017. Contains 292499 sequences.