求证：81的七次方-27的9次方-9的12次方能被45整除

81^7-27^9-9^13
=(3^4)^7-(3^3)^9-(3^2)^13
=3^28-3^27-3^26
=3^26(9-3-1)
=3^26*5
=3^2*5*3^24
=45*3^24
所以能被45整除

81^7-27^9-9^12
=1853020188851841-7625597484987-282429536481
=1845112161830373/45
=41002492485119.4有小数所以不能被整除