OJ Board

I am don't getting this problem.
Sample Input

21 2
18 2
18 18
100 7
Sample Output

21 2: 5 7 11

18 2: 3 5 7 11

18 18: 1 2 3 5 7 11 13 17

100 7: 13 17 19 23 29 31 37 41 43 47 53 59 61 67

i really don't understand the question.would somebody like to help me to get it out.