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A158453 Number of connected spanning subgraphs in 3 X n grid. 1

%I

%S 1,23,431,7857,142625,2587279,46929343,851213073,15439417633,

%T 280042119887,5079439221503,92131506968913,1671092849279201,

%U 30310492056413839,549775513106272063,9971897330025100689,180871526632046468257,3280670474584477332047

%N Number of connected spanning subgraphs in 3 X n grid.

%H Alois P. Heinz, <a href="/A158453/b158453.txt">Table of n, a(n) for n = 1..250</a>

%F G.f.: (2*x^3-x^2-x) / (54*x^3-73*x^2-1+22*x-8*x^4).

%p a:= n-> (Matrix([[23, 1, 0, 1/4]]). Matrix(4, (i, j)-> if i=j-1 then 1 elif j=1 then [22, -73, 54, -8][i] else 0 fi)^n)[1, 3]: seq(a(n), n=1..20);

%K nonn

%O 1,2

%A _Alois P. Heinz_, Mar 19 2009

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Last modified October 18 06:50 EDT 2021. Contains 348066 sequences. (Running on oeis4.)