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 A255806 Expansion of e.g.f.: exp(Sum_{k>=1} 3*x^k). 5
 1, 3, 15, 99, 801, 7623, 83079, 1017495, 13808097, 205374123, 3318673599, 57845821707, 1081091446785, 21553820597871, 456410531639799, 10225931132021247, 241609515712343361, 6002109578246918355, 156360266121378584943, 4261404847790207796147 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS In general, if e.g.f. = exp(Sum_{k>=1} m*x^k) = exp(m*x/(1-x)) and m>0, then a(n) ~ n! * m^(1/4) * exp(2*sqrt(m*n) - m/2) / (2 * sqrt(Pi) * n^(3/4)). LINKS G. C. Greubel, Table of n, a(n) for n = 0..435 FORMULA E.g.f.: exp(3*x/(1-x)). a(n) ~ 3^(1/4) * exp(2*sqrt(3*n) - 3/2) * n! / (2*sqrt(Pi)*n^(3/4)). a(n) = (2*n+1)*a(n-1) - (n-2)*(n-1)*a(n-2). - Vaclav Kotesovec, Nov 04 2016 From G. C. Greubel, Feb 24 2021: (Start) a(n) = A253286(n+3, 3). a(n) = 3*(n-1)!*LaguerreL(n-1, 1, -3) with a(0) = 1. (End) MATHEMATICA nmax=20; CoefficientList[Series[Exp[Sum[3*x^k, {k, 1, nmax}]], {x, 0, nmax}], x] * Range[0, nmax]! CoefficientList[Series[E^(3*x/(1-x)), {x, 0, 20}], x] * Range[0, 20]! Table[If[n==0, 1, 3*(n-1)!*LaguerreL[n-1, 1, -3]], {n, 0, 25}] (* G. C. Greubel, Feb 24 2021 *) PROG (PARI) my(x='x +O('x^50)); Vec(serlaplace(exp(3*x/(1-x)))) \\ G. C. Greubel, Feb 05 2017 (Sage) [1 if n==0 else 3*factorial(n-1)*gen_laguerre(n-1, 1, -3) for n in (0..25)] # G. C. Greubel, Feb 24 2021 (Magma) [n eq 0 select 1 else 3*Factorial(n-1)*Evaluate(LaguerrePolynomial(n-1, 1), -3): n in [0..25]]; // G. C. Greubel, Feb 24 2021 CROSSREFS Cf. A000262, A052897, A253286. Sequence in context: A111546 A219359 A152402 * A226515 A135883 A147664 Adjacent sequences: A255803 A255804 A255805 * A255807 A255808 A255809 KEYWORD nonn,easy AUTHOR Vaclav Kotesovec, Mar 07 2015 STATUS approved

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Last modified November 30 06:18 EST 2022. Contains 358431 sequences. (Running on oeis4.)