OFFSET
1,1
COMMENTS
For even n >= 4, also the number of minimum vertex colorings of the n-Moebius ladder.
LINKS
Eric Weisstein's World of Mathematics, Minimum Vertex Coloring.
Eric Weisstein's World of Mathematics, Moebius Ladder.
Index entries for linear recurrences with constant coefficients, signature (6,-11,6).
FORMULA
a(n) = 6*(n-1) - 11*a(n-2) + 6*a(n-3).
G.f.: 2*x*(1-6*x+6*x^2)/((-1+x)*(-1+2*x)*(-1+3*x)).
MATHEMATICA
Table[3^n - 2^(n + 1) - 1, {n, 20}]
LinearRecurrence[{6, -11, 6}, {-2, 0, 10}, 20]
CoefficientList[Series[2 (1 - 6 x + 6 x^2)/((-1 + x) (-1 + 2 x) (-1 + 3 x)), {x, 0, 20}], x]
PROG
(Python)
def A368956(n): return 3**n-(1<<n+1)-1 # Chai Wah Wu, Mar 05 2024
CROSSREFS
KEYWORD
sign,easy
AUTHOR
Eric W. Weisstein, Mar 05 2024
STATUS
approved