9 x 3 - 5 - 1 = 21
1, 3, 7, 21.
21+3 or using all the numbers: 21 + (3*(2-1))
1 x 21, 3 x 7 = 21
1, 2 and 21 when added.
1 and 147 21 and 7 3 and 49
1, 3, 7, 21: 1 x 21, 3 x 7
1, 3, 7 and 21. Four numbers.
They are members of the infinite set of numbers of the form 21*k where k is an integer.
1, 3, 7, 21
1 ,3 ,7 ,21
1, 3, 7, 21.
1, 3, 7, 21