The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 56th year, we are closing in on 350,000 sequences, and we’ve crossed 9,700 citations (which often say “discovered thanks to the OEIS”).

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A247659 Number of down-arrow-indecomposable topologies on n labeled points. 1
 1, 3, 22, 292, 6120, 193594, 9070536, 622336756, 61915861962, 8846814822932, 1798543906246948, 515674104905890202, 206833212761446463192, 115198617558900993580396, 88503974769306037986089170, 93233054587165663487254293572 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS L. Foissy and C. Malvenuto, The Hopf algebra of finite topologies and T-partitions, arXiv preprint arXiv:1407.0476, 2014 FORMULA G.f.: (A000798(x)-1)/A000798(x), where A000798(x) is the g.f. of A000798. MATHEMATICA A000798 = {1, 1, 4, 29, 355, 6942, 209527, 9535241, 642779354, 63260289423, 8977053873043, 1816846038736192, 519355571065774021, 207881393656668953041, 115617051977054267807460, 88736269118586244492485121, 93411113411710039565210494095, 134137950093337880672321868725846, 261492535743634374805066126901117203}; f[x_] = Sum[A000798[[n+1]] x^n, {n, 0, nmax = Length[A000798]-1}]; CoefficientList[(f[x]-1)/f[x] + O[x]^nmax, x][[2 ;; -2]] (* Jean-François Alcover, Oct 10 2018 *) CROSSREFS Cf. A000598, A247660. Sequence in context: A135862 A122778 A108991 * A244468 A325295 A298693 Adjacent sequences:  A247656 A247657 A247658 * A247660 A247661 A247662 KEYWORD nonn AUTHOR N. J. A. Sloane, Oct 05 2014 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 6 15:23 EST 2021. Contains 349563 sequences. (Running on oeis4.)