18
Look at the difference between each number and the next number.
24
30!
It is: 17+6 = 23
The next number in the series 7, 9, 11, 13, 15 is 17. This series is an arithmetic progression where each number increases by 2. Thus, adding 2 to the last number, 15, gives us 17.
17
This series is of the function f(x) = x2+1, starting with x=0.The next number in the series is 26. The number after that is 37.
10 11 9 12 13 8 14 7 15 6 16 5 17
17 cause it is the next prime number
129 The numbers are prime (don't consider the prefix 1)
26
14