14007941domain: NAppears in sequencesa(n) = a(n-1) + 4*a(n-2), a(0) = a(1) = 1.at n=18A006131A partial product representation of A006131 and A072265.at n=37A072270Expansion of 1/(1-x*sqrt(1+4*x^2)).at n=36A190864