a(n) = 2*a(n-1)^2 - 1, a(0)=1, a(1)=4.A084764a(n) = 2*a(n-1)^2 - 1, a(0)=1, a(1)=4.Terms a(0) =1a(1) =4a(2) =31a(3) =1921a(4) =7380481External referencesoeis: A084764