OFFSET
0,2
COMMENTS
Number of minimal edge covers in the n-book graph.
LINKS
Eric Weisstein's World of Mathematics, Book Graph
Eric Weisstein's World of Mathematics, Minimal Edge Cover
Index entries for linear recurrences with constant coefficients, signature (5, -9, 7, -2).
FORMULA
a(n) = 2*A132109(n-1).
a(n) = 5*a(n-1) - 9*a(n-2) + 7*a(n-3) - 2*a(n-4).
G.f.: -((2 x (-1 + 2 x - x^2 + x^3))/((-1 + x)^3 (-1 + 2 x))).
MATHEMATICA
Table[2^n - n + n^2, {n, 20}]
LinearRecurrence[{5, -9, 7, -2}, {2, 6, 14, 28}, 20]
CoefficientList[Series[-((2 (-1 + 2 x - x^2 + x^3))/((-1 + x)^3 (-1 + 2 x))), {x, 0, 20}], x]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Eric W. Weisstein, Aug 09 2017
EXTENSIONS
Added a(0)=0. - N. J. A. Sloane, May 25 2019
STATUS
approved