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 A196557 O.g.f.: Sum_{n>=0} 4*(n+4)^(n-1) * x^n / Product_{k=1..n} (1+k*x). 3
 1, 4, 20, 128, 1036, 10308, 122560, 1701092, 27053556, 485683128, 9723771156, 214934627476, 5201286731560, 136818097071820, 3888121468512308, 118737900886653664, 3878569457507036988, 134960059001226137588, 4984357865462772982112 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS FORMULA E.g.f.: exp(-4*LambertW(exp(-x)-1)). a(n) = Sum_{k=0..n} (-1)^(n-k)*Stirling2(n, k)*4*(k+4)^(k-1). E.g.f. A(x) = G(x)^4 where G(x) = e.g.f. of A058864, which is the number of labeled chordal graphs (connected or not) on n nodes with no induced path P_4. a(n) ~ 4*sqrt(exp(1)-1)*n^(n-1)/(exp(n-4)*(1-log(exp(1)-1))^(n-1/2)). - Vaclav Kotesovec, Jul 09 2013 EXAMPLE O.g.f.: A(x) = 1 + 4*x + 20*x^2 + 128*x^3 + 1036*x^4 + 10308*x^5 +... where the o.g.f. is given by: A(x) = 1 + 4*5^0*x/(1+x) + 4*6^1*x^2/((1+x)*(1+2*x)) + 4*7^2*x^3/((1+x)*(1+2*x)*(1+3*x)) + 4*8^3*x^4/((1+x)*(1+2*x)*(1+3*x)*(1+4*x)) +... E.g.f.: A(x) = 1 + 4*x + 20*x^2/2! + 128*x^3/3! + 1036*x^4/4! + 10308*x^5/5! +... where the e.g.f. is given by: A(x)^(1/2) = 1 + 2*x + 6*x^2/2! + 28*x^3/3! + 186*x^4/4! + 1614*x^5/5! + 17332*x^6/6! +...+ A196555(n)*x^n/n! +... A(x)^(1/4) = 1 + x + 2*x^2/2! + 8*x^3/3! + 49*x^4/4! + 402*x^5/5! + 4144*x^6/6! +...+ A058864(n)*x^n/n! +... MATHEMATICA CoefficientList[Series[E^(-4*LambertW[E^(-x)-1]), {x, 0, 20}], x]* Range[0, 20]! (* Vaclav Kotesovec, Jul 09 2013 *) PROG (PARI) {a(n)=polcoeff(sum(m=0, n, 4*(m+4)^(m-1)*x^m/prod(k=1, m, 1+k*x+x*O(x^n))), n)} (PARI) /* E.g.f. = G(x)^4 where G(x) = e.g.f. of A058864 */ {A058864(n)=polcoeff(sum(m=0, n, (m+1)^(m-1)*x^m/prod(k=1, m, 1+k*x+x*O(x^n))), n)} {a(n)=n!*polcoeff(sum(k=0, n, A058864(k)*x^k/k!+x*O(x^n))^4, n)} (PARI) {Stirling2(n, k)=if(k<0|k>n, 0, sum(i=0, k, (-1)^i*binomial(k, i)/k!*(k-i)^n))} {a(n)=sum(k=0, n, (-1)^(n-k)*Stirling2(n, k)*4*(k+4)^(k-1))} CROSSREFS Cf. A058864, A196555, A196556. Sequence in context: A007550 A080795 A126674 * A082032 A140585 A132436 Adjacent sequences:  A196554 A196555 A196556 * A196558 A196559 A196560 KEYWORD nonn AUTHOR Paul D. Hanna, Oct 03 2011 STATUS approved

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Last modified April 11 23:12 EDT 2021. Contains 342895 sequences. (Running on oeis4.)