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A158453 Number of connected spanning subgraphs in 3 X n grid. 1
1, 23, 431, 7857, 142625, 2587279, 46929343, 851213073, 15439417633, 280042119887, 5079439221503, 92131506968913, 1671092849279201, 30310492056413839, 549775513106272063, 9971897330025100689, 180871526632046468257, 3280670474584477332047 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..250

FORMULA

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

MAPLE

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);

CROSSREFS

Sequence in context: A286787 A226847 A203147 * A291128 A174262 A174425

Adjacent sequences:  A158450 A158451 A158452 * A158454 A158455 A158456

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Mar 19 2009

STATUS

approved

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Last modified September 16 15:58 EDT 2021. Contains 347473 sequences. (Running on oeis4.)