6
The factors of 21 are 1, 3, 7 and 21. No two of them add up to 21.
1 and 3
47
-117
11
The factors of 21 are 1, 3, 7 and 21. No two of them add up to 21.
1 and 3
47
-117
3 and -2 4 and -3 9 and -8
11
114, 115 & 116
The factor pairs of -3 are (-3,1)(3,-1) Neither of them add up to 5.
127
41
the prime factors of 72 are 2 and 3 6,12, and 1 (also factors) sum up to 19
12 and 1 10 and 3 9 and 4 8 and 5 various combinations of ones and twos