OFFSET
3,1
FORMULA
Empirical g.f.: -4*x^3*(8*x^3+4*x^2-2*x+1) / ((2*x+1)*(4*x^2-2*x+1)^2). - Colin Barker, Jun 20 2013
EXAMPLE
Det({ {1, 1, -1, -1, -1, -1, -1}, {1, 1, 1, -1, -1, -1, -1}, {-1, 1, 1, 1, -1, -1, -1}, {-1, -1, 1, 1, 1, -1, -1}, {-1, -1, -1, 1, 1, 1, -1}, {-1, -1, -1, -1, 1, 1, 1}, {-1, -1, -1, -1, -1, 1, 1} }=-64 => a(7)=-64
CROSSREFS
KEYWORD
sign
AUTHOR
José María Grau Ribas, Mar 25 2010
STATUS
approved