OFFSET
1,2
REFERENCES
F. Faase, On the number of specific spanning subgraphs of the graphs G X P_n, Ars Combin. 49 (1998), 129-154.
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
F. Faase, On the number of specific spanning subgraphs of the graphs G X P_n, Preliminary version of paper that appeared in Ars Combin. 49 (1998), 129-154.
F. Faase, Results from the counting program
Index entries for linear recurrences with constant coefficients, signature (6,-4,2).
FORMULA
a(n) = 6a(n-1) - 4a(n-2) + 2a(n-3), n>3.
G.f.: x*(1-x+4*x^2-2*x^3)/(1-6*x+4*x^2-2*x^3). - Colin Barker, Sep 01 2012
MATHEMATICA
CoefficientList[Series[(1 - x + 4 x^2 - 2 x^3)/(1 - 6 x + 4 x^2 - 2 x^3), {x, 0, 40}], x] (* Vincenzo Librandi, Oct 14 2013 *)
PROG
(Magma) I:=[1, 5, 30, 160]; [n le 4 select I[n] else 6*Self(n-1)-4*Self(n-2)+2*Self(n-3): n in [1..30]]; // Vincenzo Librandi, Oct 14 2013
(PARI) a(n)=([0, 1, 0; 0, 0, 1; 2, -4, 6]^(n-1)*[1; 5; 30])[1, 1] \\ Charles R Greathouse IV, Jun 23 2020
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
EXTENSIONS
More terms from Vincenzo Librandi, Oct 14 2013
STATUS
approved