OFFSET
1,1
COMMENTS
Recurrence used to extrapolate to a(1) and a(2).
LINKS
Eric Weisstein's World of Mathematics, Matching
Eric Weisstein's World of Mathematics, Maximal Independent Edge Set
Eric Weisstein's World of Mathematics, Moebius Ladder
Index entries for linear recurrences with constant coefficients, signature (1, 2, 1, -1, 2, 1, -1, -1).
FORMULA
a(n) = a(n-1)+2*a(n-2)+a(n-3)-a(n-4)+2*a(n-5)+a(n-6)-a(n-7)-a(n-8).
G.f.: x*(3-3*x^2+8*x^3+8*x^4+4*x^5-x^6-2*x^7)/(1-x-2*x^2-x^3+x^4-2*x^5-x^6+x^7+x^8).
MATHEMATICA
LinearRecurrence[{1, 2, 1, -1, 2, 1, -1, -1}, {3, 3, 6, 23, 43, 102, 213, 447, 978}, 30]
Table[2 Cos[n Pi/3] + RootSum[-1 - 2 # - #^2 + #^3 &, #^n &] - RootSum[-1 + #^2 + #^3 &, #^n &], {n, 3, 20}]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Eric W. Weisstein, Apr 01 2017
STATUS
approved