If the exponent n is 0,4,8,12,.... a multiple of 4 last(7^n)=1 If the exponent n is 1,5,9,13,.... a multiple of 4 + 1 last(7^n)=7 If the exponent n is 2,6,10,14,.... a multiple of 4 + 2 last(7^n)=9 If the exponent n is 3,7,11,15,.... a multiple of 4 + 3 last(7^n)=37