ANSWER: 9, 15, 21 are not prime numbers because these numbers have factors other than 1 and themselves. Therefore, 9, 15, 21 are composite numbersFactors of 9 other 1 and itself (9) : 3Factors of 15 other 1 and itself (15): 3, 5Factors of 21 other 1 and itself (21): 3, 7
9, 15, 21
multiples of 63
1, 3, 5, 7, 9, 15, 21, 35, 45, 63, 105, 315, -1, -3, -5, -7, -9, -15, -21, -35, -45, -63, -105, -315
12 numbers (including 21). The numbers are 4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21.
The numbers that go into 45 are 1, 3, 5, 9, 15, and 45.
1 and 3 go into both.
That's an infinite list. 9, 15, 21, 25, 27...
3, 9, 15, 21, 27, 33
63 & 5 21 & 15 9 & 35
9, 15, 21, 25, 27, 33
That's an infinite list, started by 9, 15 and 21.