13
NEXT: 11 15 16 12....
21
There are 10 possible combinations so 60 possible permutations. The combinations are:(1, 3, 21), (1, 5, 19), (1, 7, 17), (1, 9, 15), (1, 11, 13),(3, 5, 17), (3, 7, 15), (3, 9, 13), (5, 7, 13), (5, 9, 11).
2n + 1
1...2....3....43...7...11..157 - 3 = 411 - 7 = 415 - 11 = 4(the start of the nth term is 4n)4 x 1 = 4(but the first term is 3, so...)4 -1 = 3nth term = 4n - 1
1, 3, 5, 7, 9, 11, 13, 15, 17, 19. 1, 3, 5, 7, 9, 11, 13, 15, 17, 19. 1, 3, 5, 7, 9, 11, 13, 15, 17, 19. 1, 3, 5, 7, 9, 11, 13, 15, 17, 19.
16
If you mean -1 3 7 11 15 then the nth term is 4n-5 and so the next term will be 19
11 and 1/3 minus 7 and 3/5 = 56/15 or 3.73333 ..... recurring 3
11+3+1=15 but 1 is not a prime number. 3 + 5 + 7 = 15
NEXT: 11 15 16 12....
2 3 5 7 11 13 15
21
The factors of 15 are: 1, 3, 5, 15 The factors of 21 are: 1, 3, 7, 21 The factors of 33 are: 1, 3, 11, 33
2, 3, 5, 7, 11, and 13
There are 10 possible combinations so 60 possible permutations. The combinations are:(1, 3, 21), (1, 5, 19), (1, 7, 17), (1, 9, 15), (1, 11, 13),(3, 5, 17), (3, 7, 15), (3, 9, 13), (5, 7, 13), (5, 9, 11).
The sequence continues : 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31. The sequence is odd numbers of increasing length based on exponents of 2. 1 1 3 (added the next 20 numbers) 1 3 5 7 (added the next 21 = 2 numbers) 1 3 5 7 9 11 13 15 (added the next 22 = 4 numbers) 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 (added the next 23 = 8 numbers)