OFFSET
1,3
COMMENTS
Sequence extended to a(1) using formula.
LINKS
Eric Weisstein's World of Mathematics, Edge Count
Eric Weisstein's World of Mathematics, White Bishop Graph
Index entries for linear recurrences with constant coefficients, signature (2, 1, -4, 1, 2, -1).
FORMULA
a(n) = ((-1 + n)*(-3 + 3*(-1)^n - 2*n + 4*n^2))/12.
a(n) = 2*a(n-1)+a(n-2)-4*a(n-3)+a(n-4)+2*a(n-5)-a(n-6).
G.f. = x*(x + 2x^2 + 5x^3)/((-1 + x)^4*(1 + x)^2). [Corrected by Georg Fischer, May 19 2019]
MATHEMATICA
Table[(n - 1) (4 n^2 - 2 n - 3 + 3 (-1)^n)/12, {n, 20}]
LinearRecurrence[{2, 1, -4, 1, 2, -1}, {0, 1, 4, 14, 28, 55}, 20]
CoefficientList[Series[x(x + 2 x^2+ 5 x^3)/((-1 + x)^4 (1 + x)^2), {x, 0, 20}], x] (* Corrected by Georg Fischer, May 19 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Eric W. Weisstein, Jun 27 2017
STATUS
approved