A286188 Number of connected induced (non-null) subgraphs of the gear graph with 2n+1 nodes.

6, 26, 76, 218, 664, 2174, 7452, 26130, 92512, 328774, 1170052, 4166106, 14836488, 52839374, 188188396, 670240802, 2387095600, 8501764310, 30279479508, 107841961962, 384084839128, 1367938434910, 4871984975932, 17351831789874, 61799465313024

Offset: 1

Author

Giovanni Resta, May 04 2017

Keywords

• nonn

Links

• Andrew Howroyd, Table of n, a(n) for n = 1..200
• Eric Weisstein's World of Mathematics, Gear Graph
• Eric Weisstein's World of Mathematics, Vertex-Induced Subgraph
• Index entries for linear recurrences with constant coefficients, signature (6, -10, 4, 3, -2).

Crossrefs

Cf. A020873 (wheel), A059020 (ladder), A059525 (grid), A286139 (king), A286182 (prism), A286183 (antiprism), A286184 (helm), A286185 (Möbius ladder), A286186 (friendship), A286187 (web), A286188 (gear), A286189 (rook), A285765 (queen).

Programs

Mathematica

a[n_] := Block[{g = Graph@ Flatten[{Table[i <-> 2 n + 1, {i, 2, 2 n, 2}], Table[i <-> Mod[i, 2 n] + 1, {i, 2 n}]}]}, -1 + ParallelSum[ Boole@ ConnectedGraphQ@ Subgraph[g, s], {s, Subsets@ Range[2 n + 1]}]]; Array[a, 8]

Formula

a(n) = 6*a(n-1) - 10*a(n-2) + 4*a(n-3) + 3*a(n-4) - 2*a(n-5), for n>5.

a(n) = A206776(n) + 4*n^2 - 2*n + 1. - Eric W. Weisstein, May 08 2017

G.f.: 2*x*(3 - 5*x - 10*x^2 - x^3 - 3*x^4) / ((1 - x)^3*(1 - 3*x - 2*x^2)). - Colin Barker, May 31 2017

Extensions

a(16)-a(25) from Andrew Howroyd, May 20 2017