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A121720

a(n) = 4*a(n-2) - 2*a(n-4).

0, 1, 1, 3, 4, 10, 14, 34, 48, 116, 164, 396, 560, 1352, 1912, 4616, 6528, 15760, 22288, 53808, 76096, 183712, 259808, 627232, 887040, 2141504, 3028544, 7311552, 10340096, 24963200, 35303296, 85229696, 120532992, 290992384, 411525376, 993510144, 1405035520

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OFFSET

1,4

COMMENTS

For n>1, number of walks of length n-2 on the 5-vertex graph with edges {{0,1}, {1,2}, {2,3}, {2,4}} starting at vertex 3. - Sean A. Irvine, Jun 03 2025

LINKS

Table of n, a(n) for n=1..37.

Sean A. Irvine, Walks on Graphs.

Index entries for linear recurrences with constant coefficients, signature (0,4,0,-2).

FORMULA

a(n) = A007068(n-2), n>2.

G.f.: -x^2*(-1-x+x^2)/(1-4*x^2+2*x^4). [Oct 14 2009]

MATHEMATICA

LinearRecurrence[{0, 4, 0, -2}, {0, 1, 1, 3}, 30] (* Harvey P. Dale, May 21 2014 *)

CROSSREFS

Cf. A002530, A048788.

Essentially the same as A007068.