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 A120278 Sum[Sum[C(2k,k),{k,1,m}],{m,1,n}], where C(2k,k)=(2k)!/(k!)^2=A000984[k]. 1
 2, 10, 38, 136, 486, 1760, 6466, 24042, 90238, 341190, 1297574, 4958114, 19019254, 73196994, 282492254, 1092867904, 4236849774, 16455966944, 64020347914, 249431257704, 973100041934, 3800867789884, 14862066265434, 58170868424084 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(2(p-1)) is divisible by p^2 for p=7,13,19,31,37,43,61,67.. A002476 Primes of form 6n + 1. LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..200 FORMULA a(n) = Sum[Sum[(2k)!/(k!)^2,{k,1,m}],{m,1,n}]. a(n) = 2 * Sum[ A079309[k], {k,1,n} ] = Sum[ A066796[k], {k,1,n} ]. - Alexander Adamchuk, Sep 01 2006 G.f.: x*(1/Sqrt[1-4*x]-1)/(x(x-1)^2) [From Harvey P. Dale, May 24 2011] Recurrence: n*a(n) = 2*(3*n-1)*a(n-1) - (9*n-4)*a(n-2) + 2*(2*n-1)*a(n-3). - Vaclav Kotesovec, Oct 19 2012 a(n) ~ 2^(2*n+4)/(9*sqrt(Pi*n)). - Vaclav Kotesovec, Oct 19 2012 MATHEMATICA Table[Sum[Sum[(2k)!/(k!)^2, {k, 1, m}], {m, 1, n}], {n, 1, 50}] CoefficientList[Series[(1/Sqrt[1-4 x]-1)/((x-1)^2 x), {x, 0, 50}], x] (* Harvey P. Dale, May 24 2011 *) CROSSREFS Cf. A000984, A066796, A002476. Cf. A066796, A079309. Sequence in context: A281199 A056182 A081956 * A166898 A143960 A122117 Adjacent sequences:  A120275 A120276 A120277 * A120279 A120280 A120281 KEYWORD nonn AUTHOR Alexander Adamchuk, Jul 04 2006 STATUS approved

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Last modified October 16 00:50 EDT 2018. Contains 316252 sequences. (Running on oeis4.)