OFFSET
1,1
COMMENTS
For n > 2, number of irredundant sets in the (n-2)-book graph.
LINKS
Eric Weisstein's World of Mathematics, Book Graph
Eric Weisstein's World of Mathematics, Irredundant Set
Index entries for linear recurrences with constant coefficients, signature (7, -17, 17, -6).
FORMULA
a(n) = 7*a(n-1) - 17*(n-2) + 17*a(n-3) - 6*a(n-4).
G.f.: (x (4 - 22 x + 37 x^2 - 17 x^3))/((-1 + x)^2 (1 - 5 x + 6 x^2)).
MATHEMATICA
Table[5 - 2^(n - 1) + 3^(n - 1) + n - 2, {n, 20}]
LinearRecurrence[{7, -17, 17, -6}, {4, 6, 11, 26}, 20]
CoefficientList[Series[(4 - 22 x + 37 x^2 - 17 x^3)/((-1 + x)^2 (1 - 5 x + 6 x^2)), {x, 0, 20}], x]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Eric W. Weisstein, Aug 08 2017
STATUS
approved