OFFSET
1,2
COMMENTS
The radius of the n-Keller graph is 2 for n > 1. - Andrew Howroyd, Mar 23 2018
LINKS
Colin Barker, Table of n, a(n) for n = 1..1000
Eric Weisstein's World of Mathematics, Graph Distance
Eric Weisstein's World of Mathematics, Keller Graph
Index entries for linear recurrences with constant coefficients, signature (5,-7,3).
FORMULA
a(n) = 3^n + n - 1 for n > 1. - Andrew Howroyd, Mar 23 2018
From Colin Barker, Mar 24 2018: (Start)
G.f.: x^2*(5 - 3*x)*(2 - 3*x) / ((1 - x)^2*(1 - 3*x)).
a(n) = 5*a(n-1) - 7*a(n-2) + 3*a(n-3) for n>4.
(End)
PROG
(PARI) concat(0, Vec(x^2*(5 - 3*x)*(2 - 3*x) / ((1 - x)^2*(1 - 3*x)) + O(x^60))) \\ Colin Barker, Mar 24 2018
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Eric W. Weisstein, Mar 23 2018
STATUS
approved