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
Index entries for linear recurrences with constant coefficients, signature (12, -50, 80, -17, -76, 52, 16, -16).
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}]
LinearRecurrence[{12, -50, 80, -17, -76, 52, 16, -16}, {6, 33, 188, 985, 4990, 24645, 119712, 574225}, 200] (* Ray Chandler, Apr 26 2023 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Giovanni Resta, May 04 2017
EXTENSIONS
a(12)-a(24) from Andrew Howroyd, May 20 2017
STATUS
approved