余6
因
213 ÷ 7 = 30 …… 余3
27 ÷ 7 = 3……余6 等价于 27÷ 7 = 4……余-1
则
213^93 | 7
= 3^93 | 7
= (3^3)^31 | 7
= 27^31 | 7
= (-1)^31 | 7
= -1 | 7
= 6