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 A111587 a(n) = 2*a(n-1) + 2*a(n-3) + a(n-4), a(0) = 1, a(1) = 4, a(2) = 9, a(3) = 20. 1
 1, 4, 9, 20, 49, 120, 289, 696, 1681, 4060, 9801, 23660, 57121, 137904, 332929, 803760, 1940449, 4684660, 11309769, 27304196, 65918161, 159140520, 384199201, 927538920, 2239277041, 5406093004, 13051463049, 31509019100, 76069501249 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Let (b(n)) be the p-INVERT of (1,2,2,2,2,2,...) using p(S) = 1 - S^2; then b(0) = 0 and b(n) = a(n-1) for n >= 1; see A292400. - Clark Kimberling, Sep 30 2017 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (2, 0, 2, 1). FORMULA a(2n) = A090390(n+1), a(2n+1) = A046729(n+1); G.f.: (x+1)^2/((x^2+1)*(1-2*x-x^2)). [sign flipped by R. J. Mathar, Nov 10 2009] a(n) = A057077(n+1)/2 - A001333(n+2)/2. - R. J. Mathar, Nov 10 2009 MATHEMATICA LinearRecurrence[{2, 0, 2, 1}, {1, 4, 9, 20}, 30] (* Harvey P. Dale, Jul 26 2011 *) CoefficientList[Series[(x + 1)^2 / ((x^2 + 1) (1 - 2 x - x^2)), {x, 0, 33}], x] (* Vincenzo Librandi, Oct 01 2017 *) PROG Floretion Algebra Multiplication Program, FAMP Code: 2kbasekseq[J+G] with J = + j' + k' + 'ii' and G = + .5'ii' + .5'jj' + .5'kk' + .5e (MAGMA) I:=[1, 4, 9, 20]; [n le 4 select I[n] else 2*Self(n-1) +2*Self(n-3)+Self(n-4): n in [1..35]]; // Vincenzo Librandi, Oct 01 2017 CROSSREFS Cf. A019898, A046729, A090390, A111588. Sequence in context: A144685 A109110 A108870 * A161221 A130045 A225986 Adjacent sequences:  A111584 A111585 A111586 * A111588 A111589 A111590 KEYWORD easy,nonn AUTHOR Creighton Dement, Aug 08 2005 STATUS approved

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