A079162 - OEIS

A079162

a(n) = 5*a(n-2) - 2*a(n-4), with initial terms 0,1,2,4.

0, 1, 2, 4, 10, 18, 46, 82, 210, 374, 958, 1706, 4370, 7782, 19934, 35498, 90930, 161926, 414782, 738634, 1892050, 3369318, 8630686, 15369322, 39369330, 70107974, 179585278, 319801226, 819187730, 1458790182, 3736768094, 6654348458, 17045465010, 30354161926, 77753788862

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OFFSET

0,3

LINKS

Andrew Howroyd, Table of n, a(n) for n = 0..1000

Sean A. Irvine, Walks on Graphs.

Index entries for linear recurrences with constant coefficients, signature (0,5,0,-2).

FORMULA

Also a(n) = a(n-1) + 2a(n-2) if n is odd, else a(n) = 2a(n-1) + a(n-2).

a(2n) = 2*A005824(2n), a(2n+1) = A052913(n) = A005824(2n) + A005824(2n+1).

G.f.: x*(1+2*x-x^2)/(1-5*x^2+2*x^4).

MATHEMATICA