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 A126674 a(n) = n!*Sum_{j=0..n-1} 2^j/(j+1). 4
 0, 1, 4, 20, 128, 1024, 9984, 115968, 1572864, 24477696, 430571520, 8452177920, 183175741440, 4343275192320, 111817607086080, 3105593229312000, 92539365359616000, 2944365169213440000, 99619235621240832000, 3571109329517936640000, 135199252993504444416000, 5390266968989421797376000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS R. J. Mathar's recurrence is correct.  a(n) has a new sum term in addition to what a(n-1) has, giving a(n) = n*a(n-1) + 2^(n-1)*(n-1)!.  (Cf. A000165 = 2^n*n!.)  The same for a(n-1) from a(n-2), and a factor, is 2*(n-1)*(a(n-1) - (n-1)*a(n-2)) = 2^(n-1)*(n-1)! too.  Substitute it leaving a(n) in terms of a(n-1) and a(n-2).  The recurrence shows the o.g.f. satisfies the differential equation (2*x^2-x+1)*g + 3*x^2*(2*x-1)*g' + 2*x^4*g'' - x = 0. - Kevin Ryde, Jul 11 2019 LINKS N. J. A. Sloane, Notes on Carlo Wood's Polynomials FORMULA From Vladeta Jovovic, Feb 13 2007: (Start) a(n) = 2^(n-1)*A003149(n-1). O.g.f.: x*(Sum_{k>=0} k!*(2*x)^k)^2. E.g.f.: log(1-2*x)/(x-1)/2. (End) E.g.f.: E(x) = 1/2*log(1 - 2*x)/(x - 1) = x*(1 - x*G(0))/(x-1)/(2*x-1); G(k) = 1 + 2*x*(2*k+1)/(2*k + 3 - 2*x*(k+1)*(2*k+3)/(2*x*(k+1) + (k+2)/G(k+1))); (continued fraction). - Sergei N. Gladkovskii, Dec 13 2011 G.f.: x*hypergeom([1,1],[],2*x)^2. - Mark van Hoeij, May 16 2013 Conjecture: a(n) + (-3*n+2)*a(n-1) + 2*(n-1)^2*a(n-2) = 0. - R. J. Mathar, May 23 2014 G.f.: x*(1/(1 - 2*x/(1 - 2*x/(1 - 4*x/(1 - 4*x/(1 - 6*x/(1 - 6*x/(1 - ...))))))))^2. - Ilya Gutkovskiy, May 10 2017 MAPLE F:=n->add( n!*2^i/(1+i), i=0..n-1); MATHEMATICA Table[n!Sum[2^j/(j+1), {j, 0, n-1}], {n, 0, 30}] (* Harvey P. Dale, Jun 14 2017 *) PROG (MAGMA) [0] cat [Factorial(n)*(&+[2^j/(j+1):j in [0..n-1]]):n in [1..21]]; // Marius A. Burtea, Jul 12 2019 (PARI) a(n) = n!*sum(j=0, n-1, 2^j/(j+1)); \\ Michel Marcus, Jul 12 2019 CROSSREFS Row sums of A126671. Sequence in context: A135886 A007550 A080795 * A196557 A082032 A140585 Adjacent sequences:  A126671 A126672 A126673 * A126675 A126676 A126677 KEYWORD nonn AUTHOR N. J. A. Sloane and Carlo Wood (carlo(AT)alinoe.com), Feb 13 2007 STATUS approved

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Last modified April 13 19:34 EDT 2021. Contains 342941 sequences. (Running on oeis4.)