OFFSET
1,1
LINKS
Eric Weisstein's World of Mathematics, Connected Dominating Set
Eric Weisstein's World of Mathematics, Ladder Graph
Index entries for linear recurrences with constant coefficients, signature (2, 1).
FORMULA
a(n) = 4 lucas(n - 1, 2) for n > 2.
a(n) = 2*a(n-1) + a(n-2) for n > 4.
G.f.: (x (-3 - 3 x - 3 x^2 + x^3))/(-1 + 2 x + x^2).
MATHEMATICA
Table[Piecewise[{{3^n, n == 1 || n == 2}}, 4 LucasL[n - 1, 2]], {n, 20}]
Join[{3, 9}, LinearRecurrence[{2, 1}, {24, 56}, 20]]
CoefficientList[Series[(-3 - 3 x - 3 x^2 + x^3)/(-1 + 2 x + x^2), {x, 0, 20}], x]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Eric W. Weisstein, Aug 30 2017
STATUS
approved