OFFSET
1,1
COMMENTS
Also the number of chordless cycles in the n-prism graph for n >= 4.
LINKS
Eric Weisstein's World of Mathematics, Chordless Cycle
Eric Weisstein's World of Mathematics, Prism Graph
Index entries for linear recurrences with constant coefficients, signature (4, -6, 4, 0, -2, 1).
FORMULA
a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - 2*a(n-5) + a(n-6).
G.f.: x*(-3 + 8*x - 7*x^2 - 2*x^3 + 9*x^4 - 4*x^5)/((-1 + x)^2*(-1 + 2*x - x^2 + x^4)).
MATHEMATICA
Table[n + 2 Cos[n Pi/3] + LucasL[n], {n, 20}]
LinearRecurrence[{4, -6, 4, 0, -2, 1}, {3, 4, 5, 10, 17, 26}, 20]
CoefficientList[Series[(-3 + 8 x - 7 x^2 - 2 x^3 + 9 x^4 - 4 x^5)/((-1 + x)^2 (-1 + 2 x - x^2 + x^4)), {x, 0, 20}], x]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Eric W. Weisstein, Jan 02 2018
STATUS
approved