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 A274713 Number of partitions of a {3*n-1}-set into n nonempty subsets. 3
 1, 15, 966, 145750, 40075035, 17505749898, 11143554045652, 9741955019900400, 11201516780955125625, 16392038075086211019625, 29749840488672593296243236, 65580126734167548918100615020, 172597131674172062132363512309613, 534584200037719212882636004559739000, 1924887533450780657560944228447179522880, 7973126100358260458973226689851075932667520, 37645241791600906804871080818625037726247519045 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(n) is divisible by the triangular numbers: a(n) / (n*(n+1)/2) = A274712(n). LINKS Paul D. Hanna, Table of n, a(n) for n = 1..100 FORMULA O.g.f.: Sum_{n>=1} n^(3*n-1) * exp(-n^3*x) * x^n / n!, an integer series. a(n) = A008277(3*n-1,n) for n>=1, where A008277 are the Stirling numbers of the second kind. a(n) = 1/n! * Sum_{k=1..n} (-1)^(n-k) * binomial(n,k) * k^(3*n-1). a(n) = [x^(2*n-1)] 1 / Product_{k=1..n} (1 - k*x). a(n) ~ 3^(3*n-1) * n^(2*n-3/2) / (exp(2*n) * c^n * (3-c)^(2*n-1) * sqrt(2*Pi*(1-c))), where c = -LambertW(-3*exp(-3)) = 0.1785606278779211065968... = -A226750. - Vaclav Kotesovec, Jul 06 2016 EXAMPLE O.g.f.: A(x) = x + 15*x^2 + 966*x^3 + 145750*x^4 + 40075035*x^5 + 17505749898*x^6 + 11143554045652*x^7 + 9741955019900400*x^8 +... where A(x) = exp(-x)*x + 2^5*exp(-2^3*x)*x^2/2! + 3^8*exp(-3^3*x)*x^3/3! + 4^11*exp(-4^3*x)*x^4/4! + 5^14*exp(-5^3*x)*x^5/5! + 6^17*exp(-6^3*x)*x^6/6! + 7^20*exp(-7^3*x)*x^7/7! + 8^23*exp(-8^3*x)*x^8/8! +...+ n^(3*n-1)*exp(-n^3*x)*x^n/n! +... simplifies to an integer series. MATHEMATICA Table[StirlingS2[3*n - 1, n], {n, 1, 20}] (* Vaclav Kotesovec, Jul 06 2016 *) PROG (PARI) {a(n) = abs( stirling(3*n-1, n, 2) )} for(n=1, 20, print1(a(n), ", ")) (PARI) {a(n) = 1/n! * sum(k=0, n, (-1)^(n-k) * binomial(n, k) * k^(3*n-1))} for(n=1, 20, print1(a(n), ", ")) (PARI) {a(n) = polcoeff( 1/prod(k=1, n, 1-k*x +x*O(x^(2*n))), 2*n-1)} for(n=1, 20, print1(a(n), ", ")) (PARI) {a(n) = polcoeff( sum(m=1, n, m^(3*m-1) * x^m * exp(-m^3*x +x*O(x^n))/m!), n)} for(n=1, 20, print1(a(n), ", ")) CROSSREFS Cf. A129506, A217913, A274712, A008277. Sequence in context: A103639 A055413 A067408 * A229840 A102102 A196569 Adjacent sequences:  A274710 A274711 A274712 * A274714 A274715 A274716 KEYWORD nonn AUTHOR Paul D. Hanna, Jul 03 2016 STATUS approved

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Last modified December 8 14:38 EST 2019. Contains 329865 sequences. (Running on oeis4.)