24
21. Add the last 2 numbers to get the next.
From the pattern (n + 4, n + 2, n + ?) I would say the next following number is 20 (n + 1).
The next number in the sequence 5-7-13-31 is 69.
The next number will be 13+21 = 34
22
17?
15
23. They're all prime numbers
24
21. Add the last 2 numbers to get the next.
21. This is the Fibonacci series.
From the pattern (n + 4, n + 2, n + ?) I would say the next following number is 20 (n + 1).
34. Each number is the sum of the two preceding numbers. This is called the Fibonacci Sequence.
The next number in the sequence 5-7-13-31 is 69.
The numbers are decreasing by a number that decrements by 1 every time. Notice that the numbers start increasing after a while because the decrement is now a negative number. A negative negative number is positive. 18 13 9 6 4 3 3 4 6 ...
If you mean: 1 2 3 5 8 13 then the next number is 8+13 = 21