18571329536domain: NAppears in sequencesa(n) = 2*a(n-1) + 4*a(n-2); with a(0)=1, a(1)=4.at n=20A087206a(n) = 4^(n-1)*U(n-1, 3/2) where U is the Chebyshev polynomial of the second kind.at n=11A099157a(n) = -2*a(n-1)+4*a(n-2), n>1 ; a(0) = 1, a(1) = -4.at n=20A152174