581984768domain: NAppears in sequencesa(0) = 1, a(1) = 2, a(n) = 4*a(n-1) - 2*a(n-2), n >= 2.at n=17A006012Expansion of g.f. (1 + x - 2*x^2 - x^3)/(1/2 - 2*x^2 + x^4).at n=33A030435Expansion of g.f. (1 + x - 2*x^2 - x^3)/(1 - 4*x^2 + 2*x^4).at n=34A030436a(n) = coefficient of x in (1+x)^n mod (1+x^4).at n=34A099587