OFFSET
0,2
COMMENTS
For n>= 3, a(n) is the second Zagreb index of the wheel graph with n+1 vertices. The second Zagreb index of a simple connected graph is the sum of the degree products d(i)d(j) over all edges ij of g.
LINKS
Leo Tavares, Illustration: Hexagonal Stars
Index entries for linear recurrences with constant coefficients, signature (3,-3,1).
FORMULA
EXAMPLE
a(3) = 54. Indeed, the wheel graph with 4 vertices consists of 6 edges, each connecting two vertices of degree 3. Then, the second Zagreb index is 6*3*3 = 54.
MAPLE
seq(3*n*(n+3), n = 0 .. 45);
MATHEMATICA
PROG
(PARI) a(n)=3*n*(n+3) \\ Charles R Greathouse IV, Jun 17 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Emeric Deutsch, Nov 08 2016
STATUS
approved