16218279010domain: NAppears in sequencesa(0)=1, a(1)=1, a(2)=1, a(n) = 2*a(n-1) + a(n-2) + 1.at n=28A033539Expansion of (1 + 3*x - 2*x^2)/(1 - 7*x + 7*x^2 - x^3).at n=13A301383