=9^m+1*(3*9)^m-1
=9^m+1*9^m-1*3^m-1
=9^m=m+1-1*3^m-1
=9^2m*3^m-1
=3^4m*3^m-1
=3^4m+m-1
=3^5m-1
^如果是幂的意思,应该是这么做.