3的45次方除以7余数是3
3^45
=3*3^44
=3*81^11
=243*81^10
=243*6561^5
个位数是3,
561^5
=561*561^4
=561*3921^2
921*921
=848241
243*241
=58563
563*561
=315843
315843/7=4520.3