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 A102591 a(n) = Sum_{k=0..n} binomial(2n+1, 2k)*3^(n-k). 10
 1, 6, 44, 328, 2448, 18272, 136384, 1017984, 7598336, 56714752, 423324672, 3159738368, 23584608256, 176037912576, 1313964867584, 9807567290368, 73204678852608, 546407161659392, 4078438577864704, 30441879976280064 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS In general, Sum_{k=0..n} binomial(2n+1,2k)*r^(n-k) has g.f. (1-(r-1)x)/(1-2(r+1)+(r-1)^2x^2) and a(n) = ((sqrt(r)-1)^(2n+1) + (sqrt(r)+1)^(2n+1))/(2*sqrt(r)). LINKS Index entries for linear recurrences with constant coefficients, signature (8,-4). FORMULA G.f.: (1-2x)/(1-8x+4x^2); a(n) = 8*a(n-1) - 4*a(n-2); a(n) = sqrt(3)*(sqrt(3)-1)^(2n+1)/6 + sqrt(3)*(sqrt(3)+1)^(2n+1)/6. a(n) = 2^n*A079935(n). - R. J. Mathar, Sep 20 2012 a(n) = 2^(2*n+1)*Sum_{k >= n} binomial(2*k,2*n)*(1/3)^(k+1). Cf. A099156. - Peter Bala, Nov 29 2021 MATHEMATICA LinearRecurrence[{8, -4}, {1, 6}, 20] (* Harvey P. Dale, Sep 28 2021 *) CROSSREFS Bisection of A080879 or A002605. Cf. A066443, A099156, A102592. Sequence in context: A091163 A189800 A227665 * A114935 A115969 A082412 Adjacent sequences: A102588 A102589 A102590 * A102592 A102593 A102594 KEYWORD easy,nonn AUTHOR Paul Barry, Jan 22 2005 STATUS approved

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Last modified December 7 05:41 EST 2022. Contains 358649 sequences. (Running on oeis4.)