OFFSET
1,3
EXAMPLE
a(3)=6 because there are 6 different irreducible characteristic polynomials of 3 x 3 binary robust matrices: -1-2y-y^2+y^3,-1-2y-y^2+y^3, -1-y-y^2+y^3, -1+y-2y^2+y^3, -1+2y-3y^2+y^3, 1-y-2y^2+y^3.
CROSSREFS
KEYWORD
nonn
AUTHOR
Artur Jasinski and Peter Pein (petsie(AT)dordos.net), Jan 07 2007
STATUS
approved