1254464domain: NAppears in sequencesa(0) = 1, a(1) = 2, a(n) = 4*a(n-1) - 2*a(n-2), n >= 2.at n=12A006012Expansion of g.f. (1 + x - 2*x^2 - x^3)/(1/2 - 2*x^2 + x^4).at n=23A030435Expansion of g.f. (1 + x - 2*x^2 - x^3)/(1 - 4*x^2 + 2*x^4).at n=24A030436a(0)=0; a(1)=1; a(n) = a(n-1) + (3 + (-1)^n)*a(n-2)/2.at n=25A062112