17 cause it is the next prime number
18. 3+1=4, 4+2=6, 6+3=9, 9+4=13, 13+5=18.
The next number is 13... you're adding the previous two numbers together to produce the next in line.
Answer = 21 The next number is the previous 2 numbers added together
11 comes next.
18
17 cause it is the next prime number
31
the next number is 21 because it is adding the last number stated.
34
17
13, because if you add the last number to the current number you get the next number
13 because each time it goes 1 odd number up.
18. 3+1=4, 4+2=6, 6+3=9, 9+4=13, 13+5=18.
The next number is 13... you're adding the previous two numbers together to produce the next in line.
These are Fibannoci's numbers. Therefore, the 7th number is 21.
15? ================= I'm guessing this is a list of the prime numbers? So the next number would be 17.