65
33
17
15? ================= I'm guessing this is a list of the prime numbers? So the next number would be 17.
It is 129.
29
65
17 cause it is the next prime number
33
Big numbers can be difficult to factor. You know 2 isn't a factor because it's not an even number. You know 3 isn't a factor because the sum of digits 2+4+5+3 = 14 is not a multiple of 3. You know 5 isn't, either, because it doesn't end in 5 or 0. Next try 7 - also not a factor. The next prime to try is 11: 2453 = 11 * 223 Now we're getting somewhere. Is 223 prime? The next factor to test for is 13. It is not a factor of 223. We can quit now because the next prime is 17, and 17^2 > 223. So 223 is prime. So the answer is simply 2453 = 11 * 223
33
28 (add on the prime number 11)
143
14
17 is a prime number - the next composite number after 17 is 18.
17
17