A286187 Number of connected induced (non-null) subgraphs of the web graph with 3n nodes.

6, 33, 188, 985, 4990, 24645, 119712, 574225, 2727218, 12847821, 60115060, 279652793, 1294441894, 5965567125, 27387631368, 125308264225, 571591760602, 2600204421405, 11799376912220, 53424388364873, 241398575303374, 1088727972172389, 4901842528232304, 22034981672761649

Offset

1,1

Links

Andrew Howroyd, Table of n, a(n) for n = 1..200

Eric Weisstein's World of Mathematics, Vertex-Induced Subgraph

Eric Weisstein's World of Mathematics, Web Graph

Formula

Empirical g.f.: x*(6 - 39*x + 92*x^2 - 101*x^3 + 32*x^4 - 8*x^5 + 64*x^6 - 48*x^7) / ((1 - x)^2*(1 - 5*x + 2*x^2 + 4*x^3)^2). - Colin Barker, May 21 2017

Mathematica

{6, 33} ~Join~ Table[g = GraphData[{"Web", n}]; -1 + ParallelSum[Boole@ ConnectedGraphQ@ Subgraph[g, s], {s, Subsets@ Range[3 n]}], {n, 3, 6}]

Crossrefs

Cf. A020873 (wheel), A059020 (ladder), A059525 (grid), A286139 (king), A286182 (prism), A286183 (antiprism), A286184 (helm), A286185 (Möbius ladder), A286186 (friendship), A286188 (gear), A286189 (rook), A285765 (queen).

Sequence in context: A180035 A360717 A379139 * A260774 A218182 A093964

Adjacent sequences: A286184 A286185 A286186 * A286188 A286189 A286190

Keyword

nonn,changed

Author

Giovanni Resta, May 04 2017

Extensions

a(12)-a(24) from Andrew Howroyd, May 20 2017

Status

approved