OFFSET
1,3
LINKS
Eric Weisstein's World of Mathematics, Graph Cycle
Eric Weisstein's World of Mathematics, Rook Graph
Index entries for linear recurrences with constant coefficients, signature (7, -21, 35, -35, 21, -7, 1).
FORMULA
a(n) = 6*n*binomial(n,3)*(n^2-2*n+7)/5.
a(n) = 7*a(n-1)-21*a(n-2)+35*a(n-3)-35*a(n-4)+21*a(n-5)-7*a(n-6)+a(n-7).
G.f.: (-12*x^3*(3+3*x+5*x^2+x^3))/(-1+x)^7.
MATHEMATICA
Table[(n - 2) (n - 1) n^2 (n^2 - 2 n + 7)/5, {n, 20}]
Table[6 n Binomial[n, 3] (n^2 - 2 n + 7)/5, {n, 20}]
LinearRecurrence[{7, -21, 35, -35, 21, -7, 1}, {0, 0, 36, 288, 1320, 4464, 12348}, 20]
CoefficientList[Series[-((12 x^2 (3 + 3 x + 5 x^2 + x^3))/(-1 + x)^7), {x, 0, 20}], x]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Eric W. Weisstein, Jun 20 2017
STATUS
approved