7+3=10 17+3=20 17+13=30
-20
They are: 2+7+11 = 20
3 and 17
600 * * * * * It is, in fact, 639
7+3=10 17+3=20 17+13=30
-20
148
It is 75.
They are: 2+7+11 = 20
17 and 3 are two prime numbers whose sum is 20. Their product is 51.
3 and 17
600 * * * * * It is, in fact, 639
17
It is 1.
(2,3) and (2,5) are the two pairs such that the sum of their elements is a prime number.
The sum is: 23+29+31+37 = 120