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 A227207 E.g.f.: Sum_{n>=0} n^n * x^n / (n! * Product_{k=0..n} (1 - n*k*x)). 0
 1, 1, 6, 105, 3568, 204745, 18028266, 2278860535, 394667414016, 90302033890953, 26525942216131330, 9775058594870836861, 4433256936788979640848, 2434899483389881601250937, 1597444746833206096334387802, 1237091666097626095124512681755, 1119205949224015886848972396596736 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS FORMULA Sum_{n>=0} a(n)*x^n / n!^2  =  Sum_{n>=0} (exp(n*x) - 1)^n / n!^2. a(n) = n! * Sum_{k=0..n} k^n * Stirling2(n,k) / k!. EXAMPLE E.g.f.: A(x) = 1 + x + 6*x^2/2! + 105*x^3/3! + 3568*x^4/4! + 204745*x^5/5! +... where A(x) = 1 + x/(1-x) + 2^2*x^2/(2!*(1-2*1*x)*(1-2*2*x)) + 3^3*x^3/(3!*(1-3*1*x)*(1-3*2*x)*(1-3*3*x)) + 4^4*x^4/(4!*(1-4*1*x)*(1-4*2*x)*(1-4*3*x)*(1-4*4*x)) +... MATHEMATICA Flatten[{1, Table[n! * Sum[k^n * StirlingS2[n, k] / k!, {k, 0, n}], {n, 1, 20}]}] (* Vaclav Kotesovec, May 08 2014 *) PROG (PARI) {a(n)=n!*polcoeff(sum(m=0, 20, m^m*x^m/m!/prod(k=1, m, 1-m*k*x +x*O(x^n))), n)} for(n=0, 20, print1(a(n), ", ")) (PARI) {a(n)=n!^2*polcoeff(sum(m=0, n, (exp(m*x+x*O(x^n))-1)^m/m!^2), n)} for(n=0, 20, print1(a(n), ", ")) (PARI) {Stirling2(n, k)=n!*polcoeff(((exp(x+x*O(x^n))-1)^k)/k!, n)} {a(n)=n!*sum(k=0, n, k^n*Stirling2(n, k)/k!)} for(n=0, 20, print1(a(n), ", ")) CROSSREFS Cf. A119392, A229257, A229258, A229259, A229260, A229261. Cf. A229233, A229234, A220181, A122399. Sequence in context: A309378 A221933 A110342 * A126467 A013294 A013300 Adjacent sequences:  A227204 A227205 A227206 * A227208 A227209 A227210 KEYWORD nonn AUTHOR Paul D. Hanna, Sep 18 2013 STATUS approved

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Last modified August 2 08:04 EDT 2021. Contains 346422 sequences. (Running on oeis4.)