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 A304400 O.g.f. A(x) satisfies: [x^n] exp( n^2 * x*A(x) ) * (2 - A(x)) = 0 for n > 0. 5
 1, 1, 8, 153, 4736, 205125, 11606832, 826208992, 72258829312, 7635270104361, 961709587281200, 142709474491679777, 24684776053129473408, 4928830965337886481836, 1126011129156595573835552, 291967631033958376653342600, 85304359600279978669204291584, 27900684466477404020849587348577 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Note: the factorial series, F(x) = Sum_{n>=0} n! * x^n, satisfies: (1) [x^n] exp( n * x*F(x) ) * (2 - F(x)) = 0 for n > 0, (2) [x^n] exp( x*F(x) ) * (n + 1 - F(x)) = 0 for n > 0. It is remarkable that this sequence should consist entirely of integers. A304857(n) = a(n) / n^2 for n >= 1. LINKS Paul D. Hanna, Table of n, a(n) for n = 0..300 FORMULA a(n) ~ c * n!^2 * n^2, where c = 0.777184293541721432034108670879422244... - Vaclav Kotesovec, Oct 06 2020 EXAMPLE O.g.f.: A(x) = 1 + x + 8*x^2 + 153*x^3 + 4736*x^4 + 205125*x^5 + 11606832*x^6 + 826208992*x^7 + 72258829312*x^8 + 7635270104361*x^9 + ... ILLUSTRATION OF DEFINITION. The table of coefficients of x^k/k! in exp( n^2 * x*A(x) ) * (2 - A(x)) begins: n=0: [1, -1, -16, -918, -113664, -24615000, -8356919040, ...]; n=1: [1, 0, -15, -920, -113955, -24650904, -8363901035, ...]; n=2: [1, 3, 0, -830, -113088, -24636696, -8363675648, ...]; n=3: [1, 8, 65, 0, -97923, -23962896, -8273887803, ...]; n=4: [1, 15, 240, 3850, 0, -19894104, -7851595520, ...]; n=5: [1, 24, 609, 16432, 444861, 0, -6241325915, ...]; n=6: [1, 35, 1280, 49410, 2034240, 84952296, 0, ...]; n=7: [1, 48, 2385, 123640, 6775197, 399396504, 24384667957, 0, ...]; ... in which the main diagonal is all zeros after the initial term, illustrating that [x^n] exp( n^2 * x*A(x) ) * (2 - A(x)) = 0 for n > 0. Terms along the secondary diagonal in the above table are divisible by the odd numbers: [1, 3/3, 65/5, 3850/7, 444861/9, 84952296/11, 24384667957/13, ...] = [1, 1, 13, 550, 49429, 7722936, 1875743689, ...]. RELATED SERIES. exp( x*A(x) ) = 1 + x + 3*x^2/2! + 55*x^3/3! + 3889*x^4/4! + 588201*x^5/5! + 151295251*x^6/6! + 59575340623*x^7/7! + 33795420271425*x^8/8! + ... Note that the factorial series F(x) = 1 + x + 2!*x^2 + 3!*x^3 + 4!*x^4 + 5!*x^5 + ... + n!*x^n + ... satisfies [x^n] exp( n*x*F(x) ) * (2 - F(x)) = 0 for n > 0. PROG (PARI) {a(n) = my(A=[1], m); for(i=1, n, A=concat(A, 0); m=#A; A[m] = Vec( exp( (m-1)^2 * x * Ser(A) ) * (2 - Ser(A)) )[m] ); A[n+1]} for(n=0, 20, print1(a(n), ", ")) CROSSREFS Cf. A304401, A304402, A304857, A305116. Sequence in context: A094059 A171202 A247538 * A174845 A302259 A113268 Adjacent sequences:  A304397 A304398 A304399 * A304401 A304402 A304403 KEYWORD nonn AUTHOR Paul D. Hanna, May 25 2018 STATUS approved

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Last modified December 6 04:52 EST 2021. Contains 349562 sequences. (Running on oeis4.)