27959497216domain: NAppears in sequencesa(0) = 1, a(1) = 2, for n > 1, a(n) = 4*a(n-1) - 2*a(n-2).at n=20A003480Pisot sequence P(2,7): a(0)=2, a(1)=7, thereafter a(n+1) is the nearest integer to a(n)^2/a(n-1).at n=19A020727Expansion of (1+2*x-x^3)/(1-4*x^2+2*x^4).at n=39A217730