The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A247660 Number of bi-indecomposable topologies on n labeled points. 1
 1, 2, 15, 229, 5298, 177661, 8605831, 601894158, 60571434501, 8716575772821, 1780241773757704, 511992638746006383, 205785031866223973343, 114780183140747719353332, 88271680420025831479693219, 93054995762621287409298093049 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Table of n, a(n) for n=1..16. L. Foissy and C. Malvenuto, The Hopf algebra of finite topologies and T-partitions, arXiv preprint arXiv:1407.0476 [math.RA], 2014. FORMULA G.f.: (-2+3*f(x)-f(x)^2)/f(x), where f(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[(-2 + 3 f[x] - f[x]^2)/f[x] + O[x]^nmax, x][[2 ;; -2]] (* Jean-François Alcover, Oct 10 2018 *) CROSSREFS Cf. A000598, A247659. Sequence in context: A184357 A090301 A297087 * A197236 A097628 A305111 Adjacent sequences: A247657 A247658 A247659 * A247661 A247662 A247663 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 | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified August 10 16:53 EDT 2024. Contains 375058 sequences. (Running on oeis4.)