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 A092366 Coefficient of x^n in expansion of (1+n*x+n*x^2)^n. 11
 1, 1, 8, 81, 1120, 19375, 400896, 9630411, 262955008, 8032730715, 271175200000, 10017828457483, 401738097475584, 17371952344599385, 805429080795852800, 39844314853048828125, 2094272851244149112832, 116526044312704751752451 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Also coefficient of x^n in expansion of (1-2*n*x+(n^2-4*n)*x^2)^(-1/2). - Vladeta Jovovic, Mar 22 2004 LINKS Seiichi Manyama, Table of n, a(n) for n = 0..381 (terms 1..100 from Vincenzo Librandi) FORMULA a(n) = n^(n/2)*GegenbauerPoly(n,-n,-sqrt(n)/2). - Emanuele Munarini, Oct 20 2016 Sum_{k=floor(n/2)..n} n^k*binomial(n, k)*binomial(k, n-k). - Vladeta Jovovic, Mar 22 2004 a(n) ~ n^(n-1/4) * exp(2*sqrt(n)-2) / (2*sqrt(Pi)). - Vaclav Kotesovec, Apr 17 2014 MAPLE seq(n!*coeff(series(exp(n*x)*BesselI(0, 2*sqrt(n)*x), x, n+1), x, n), n=1..17); MATHEMATICA Table[Sum[n^k*Binomial[n, k]*Binomial[k, n-k], {k, Floor[n/2], n}], {n, 1, 20}] (* Vaclav Kotesovec, Apr 17 2014 *) Table[If[n == 0, 1, n^(n/2) GegenbauerC[n, -n, -Sqrt[n]/2]], {n, 0, 12}] (* Emanuele Munarini, Oct 20 2016 *) PROG (PARI) q(n)=(1+n*x+n*x^2)^n; for(i=0, 20, print1(", "polcoeff(q(i), i))) (MAGMA) P:=PolynomialRing(Integers()); [ Coefficients((1+n*x+n*x^2)^n)[n+1]: n in [1..22] ]; // Klaus Brockhaus, Mar 03 2011 (Maxima) a(n):=coeff(expand((1+n*x+n*x^2)^n), x, n); makelist(a(n), n, 1, 12); /* Emanuele Munarini, Mar 02 2011 */ CROSSREFS Cf. A186925, A187018. Sequence in context: A007778 A065440 A318047 * A022519 A138439 A193563 Adjacent sequences:  A092363 A092364 A092365 * A092367 A092368 A092369 KEYWORD nonn AUTHOR Jon Perry, Mar 19 2004 EXTENSIONS a(0)=1 prepended by Seiichi Manyama, May 01 2019 STATUS approved

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Last modified October 16 03:37 EDT 2019. Contains 328040 sequences. (Running on oeis4.)