Prime numbers mean that their factors are only the number itself and 1.
2, 3, 5, 7, 11, etc. all fall under this category.
note however, that the numbers have to be less than 8: [2, 3, 5, 7] are your choices
2 + 3 = 5
5 + 5 = 10
10 + 7 = 17
Therefore, {2, 3, 5, 7} are your answers
hope this helps