OFFSET
1,2
COMMENTS
Extended to a(1) using formula/recurrence.
LINKS
Eric Weisstein's World of Mathematics, Chromatic Invariant
Eric Weisstein's World of Mathematics, Crossed Prism Graph
Index entries for linear recurrences with constant coefficients, signature (9, -24, 20).
FORMULA
a(n) = 5^n - 2^(n - 1)*(3*n + 1).
a(n) = 9*a(n-1) - 24*a(n-2) + 20*a(n-3).
G.f. = x*(-1 - 2*x - 10*x^2)/((-1 + 2*x)^2 (-1 + 5*x)).
MATHEMATICA
Table[5^n - 2^(n - 1) (3 n + 1), {n, 20}]
LinearRecurrence[{9, -24, 20}, {1, 11, 85}, 20]
CoefficientList[Series[(-1 - 2 x - 10 x^2)/((-1 + 2 x)^2 (-1 + 5 x)), {x, 0, 20}], x]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Eric W. Weisstein, Nov 16 2017
STATUS
approved