a(n) = ((2*n)^(2*n+2) - 1)/(4*n^2 - 1).A066210a(n) = ((2*n)^(2*n+2) - 1)/(4*n^2 - 1).Terms a(0) =1a(1) =5a(2) =273a(3) =47989a(4) =17043521a(5) =10101010101External referencesoeis: A066210