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 A162161 E.g.f. satisfies: A(x) = exp(x + x^2 + x^3*A(x)). 2
 1, 1, 3, 13, 73, 561, 5251, 57583, 739089, 10794241, 176570371, 3209512791, 64116701353, 1396247370961, 32941566738627, 836962322583871, 22785381648804001, 661810614930630273, 20428823103775758595 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS FORMULA a(n) = n!*Sum_{k=0..n} Sum(j=0..k} (j+1)^(n-k-1)/(n-k)! * C(n-k,k-j)*C(k-j,j). Let A(x)^m = Sum_{n>=0} a(n,m)*x^n/n!, then a(n) = n!*Sum_{k=0..n} Sum(j=0..k} m*(j+m)^(n-k-1)/(n-k)! * C(n-k,k-j)*C(k-j,j). E.g.f.: A(x) = exp(x*F(x)) where F(x) is the e.g.f. of A162697. [From Paul D. Hanna, Jul 18 2009] E.g.f.: -LambertW(-exp(x*(1+x))*x^3)/x^3. - Vaclav Kotesovec, Jan 10 2014 a(n) ~ sqrt(2*r^2+r+3) * n^(n-1) / (exp(n) * r^(n+3)), where r = 0.542223654754281322169639... is the root of the equation exp(r^2+r+1)*r^3 = 1. - Vaclav Kotesovec, Jan 10 2014 EXAMPLE E.g.f.: A(x) = 1 + x + 3*x^2/2! + 13*x^3/3! + 73*x^4/4! + 561*x^5/5! +... MATHEMATICA CoefficientList[Series[-ProductLog[-E^(x*(1+x))*x^3]/x^3, {x, 0, 20}], x] * Range[0, 20]! (* Vaclav Kotesovec, Jan 10 2014 *) PROG (PARI) {a(n, m=1)=n!*sum(k=0, n, sum(j=0, k, m*(j+m)^(n-k-1)/(n-k)!*binomial(n-k, k-j)*binomial(k-j, j)))} CROSSREFS Cf. A162697. [From Paul D. Hanna, Jul 18 2009] Sequence in context: A124468 A205572 A128196 * A119013 A190878 A156154 Adjacent sequences:  A162158 A162159 A162160 * A162162 A162163 A162164 KEYWORD nonn AUTHOR Paul D. Hanna, Jun 26 2009 STATUS approved

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Last modified October 14 11:36 EDT 2019. Contains 327996 sequences. (Running on oeis4.)