由于a1*a2*a3*...*an=n^2 ------(1)则:a1*a2*a3*...*a(n-1)=(n-1)^2 ------(2)(1)/(2)得:an=n^2/[(n-1)^2]则:a3=3^2/[(3-1)^2]=9/4a5=5^2/[(5-1)^2]=25/16a3+a5=9/4+25/16=61/16