OFFSET
3,2
LINKS
John Konvalina, On the number of combinations without unit separation, Journal of Combinatorial Theory, Series A 31.2 (1981): 101-107. See Table II, row k=2.
Eric Weisstein's World of Mathematics, Cycle Complement Graph
Eric Weisstein's World of Mathematics, Minimum Dominating Set
Index entries for linear recurrences with constant coefficients, signature (3,-3,1).
FORMULA
a(n) = n*(n - 3)/2 for n > 4.
G.f.: x^3*(-1 - x + 4*x^2 - 5*x^3 + 2*x^4)/(-1 + x)^3.
From Stefano Spezia, Sep 08 2021: (Start)
E.g.f.: x*(12 + 6*exp(x)*(x - 2) + 6*x + 2*x^2 + x^3)/12.
a(n) = 3*a(n-1) - 3*a(n-3) + a(n-3) for n > 4. (End)
MATHEMATICA
Join[{1, 4}, Table[n(n-3)/2, {n, 5, 20}]]
CoefficientList[Series[x^3(-1 - x + 4 x^2 - 5 x^3 + 2 x^4)/(-1 + x)^3, {x, 0, 20}], x]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Eric W. Weisstein, Sep 06 2021
STATUS
approved