a(n) = ((2n)^(2n-1)+1)/(2n+1).A128897a(n) = ((2n)^(2n-1)+1)/(2n+1).Terms a(0) =1a(1) =13a(2) =1111a(3) =233017a(4) =90909091a(5) =57154490053External referencesoeis: A128897