OFFSET
1,1
LINKS
FORMULA
G.f.: (2*z*(1+z)*(1-z)^3)/(1-7z+9z^2+z^3-9z^4+3z^5).
EXAMPLE
The only diglasses that are not row convex are "two mountains" and its 180-degree rotation. So a(2) = A319324(2) - 2 = 10.
MATHEMATICA
Rest@CoefficientList[Series[(2z(1+z)(1-z)^3)/(1-7z+9z^2+z^3-9z^4+3z^5), {z, 0, 20}], z]
CROSSREFS
KEYWORD
nonn
AUTHOR
David Bevan, Sep 27 2018
STATUS
approved