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 A268147 A double binomial sum involving absolute values. 4
 0, 16, 512, 12288, 262144, 5242880, 100663296, 1879048192, 34359738368, 618475290624, 10995116277760, 193514046488576, 3377699720527872, 58546795155816448, 1008806316530991104, 17293822569102704640, 295147905179352825856, 5017514388048998039552 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS A fast algorithm follows from Theorem 1 of Brent et al. article. LINKS Colin Barker, Table of n, a(n) for n = 0..800 Richard P. Brent, Hideyuki Ohtsuka, Judy-anne H. Osborn, Helmut Prodinger, Some binomial sums involving absolute values, arXiv:1411.1477v2 [math.CO], 2016. Index entries for linear recurrences with constant coefficients, signature (32,-256). FORMULA a(n) = Sum_{k=-n..n} (Sum_{l=-n..n} binomial(2*n, n+k)*binomial(2*n, n+l)*abs(k-l)^2). From Colin Barker, Feb 11 2016: (Start) a(n) = n*16^n. a(n) = 32*a(n-1)-256*a(n-2) for n>1. G.f.: 16*x / (1-16*x)^2. (End) MAPLE a:= proc(n) option remember; 16*`if`(n<2, n, n*a(n-1)/(n-1)) end: seq(a(n), n=0..20); # Alois P. Heinz, Jan 29 2016 MATHEMATICA Table[n*16^n, {n, 0, 20}] (* Jean-François Alcover, Oct 24 2016 *) LinearRecurrence[{32, -256}, {0, 16}, 20] (* Harvey P. Dale, Jul 19 2018 *) PROG (PARI) a(n) = sum(k=-n, n, sum(l=-n, n, binomial(2*n, n+k)*binomial(2*n, n+l)*abs(k-l)^2)); (PARI) concat(0, Vec(16*x/(1-16*x)^2 + O(x^20))) \\ Colin Barker, Feb 11 2016 (PARI) a(n)=n*16^n \\ Charles R Greathouse IV, May 10 2016 CROSSREFS Cf. A000984, A002894, A166337. Sequence in context: A302744 A147641 A300801 * A303453 A303459 A301440 Adjacent sequences: A268144 A268145 A268146 * A268148 A268149 A268150 KEYWORD easy,nonn AUTHOR Richard P. Brent, Jan 27 2016 STATUS approved

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Last modified January 30 22:27 EST 2023. Contains 359947 sequences. (Running on oeis4.)