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 A055990 a(n) is its own 4th difference. 5
 1, 4, 14, 50, 181, 657, 2385, 8657, 31422, 114051, 413966, 1502555, 5453761, 19795288, 71850128, 260791401, 946583628, 3435774958, 12470688498, 45264335853, 164294064481, 596331286321, 2164478699633, 7856317702310 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 Index entries for linear recurrences with constant coefficients, signature (5,-6,4,-1). FORMULA a(n) = 5*a(n-1)-6*a(n-2)+4*a(n-3)-a(n-4) = a(n-1)+A055989(n) = A055991(n)-A055991(n-1) = A055988(n+1)-2*A055988(n)+A055988(n-1). G.f.: x*(1-x)/(1-5*x+6*x^2-4*x^3+x^4). [Colin Barker, Apr 05 2012] a(n) = Sum_{m=0..n-1} C(n+3m+1,n-m-1). - Vladimir Kruchinin, Nov 18 2020 MATHEMATICA CoefficientList[Series[(1-x)/(1-5*x+6*x^2-4*x^3+x^4), {x, 0, 30}], x] (* Vincenzo Librandi, Apr 06 2012 *) LinearRecurrence[{5, -6, 4, -1}, {1, 4, 14, 50}, 30] (* Harvey P. Dale, Oct 18 2015 *) PROG (Magma) I:=[1, 4, 14, 50]; [n le 4 select I[n] else 5*Self(n-1)-6*Self(n-2)+4*Self(n-3)-Self(n-4): n in [1..30]]: // Vincenzo Librandi, Apr 06 2012 (PARI) Vec((1-x)/(1-5*x+6*x^2-4*x^3+x^4)+O(x^99)) \\ Charles R Greathouse IV, Apr 06 2012 (Maxima) a(n):=sum((binomial(n+3*m+1, n-m-1)), m, 0, n-1); /* Vladimir Kruchinin, Nov 18 2020 */ CROSSREFS Cf. A055988, A055989, A055991 for the other differences of a(n). See A000079, A001906, A052529 for examples of sequences which are respectively their own first, second and third differences. Sequence in context: A211304 A047065 A047008 * A211308 A087945 A051924 Adjacent sequences:  A055987 A055988 A055989 * A055991 A055992 A055993 KEYWORD nonn,easy AUTHOR Henry Bottomley, Jun 02 2000 EXTENSIONS More terms from James A. Sellers, Jun 05 2000 STATUS approved

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Last modified November 26 04:03 EST 2022. Contains 358353 sequences. (Running on oeis4.)