求证：1+3^3n+1+9^3n+1 （n属于N*）能被13整除
1+3^3n+1+9^3n+1
=3^0+3^3n+3^9n+3^0
= log3 3 +log3 3^(3^3n) +log3 3^(3^9n)+log3 3
=log3 (3^1 * 3^(3^3n) * 3^(3^9n) *3^1 )