a(n) = ((2^n - 1)^(2^n) - 1)/(2^n)^2.A123591a(n) = ((2^n - 1)^(2^n) - 1)/(2^n)^2.Terms a(0) =-1a(1) =0a(2) =5a(3) =90075External referencesoeis: A123591