93222357domain: NAppears in sequencesNumber of polynomials of height n: a(1)=1, a(2)=1, a(3)=4, a(n) = 2*a(n-1) + a(n-2) + 2 for n >= 4.at n=21A005409Expansion of g.f. (1+8*x-x^2)/((1+x)*(1-6*x+x^2)).at n=10A105058