21. Add the last 2 numbers to get the next.
24
The next number in the sequence 5-7-13-31 is 69.
From the pattern (n + 4, n + 2, n + ?) I would say the next following number is 20 (n + 1).
The nest number in the sequence is 18. Note that the difference between each number and the next number in the sequence follows the simple sequence of 1,2,3,4. Obviously the next in the sequence of increases is 5, so 13+5=18.
The pattern is plus 7. So the next number used to be 1.
22
23. They're all prime numbers
24
15
17?
21. This is the Fibonacci series.
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.
From the pattern (n + 4, n + 2, n + ?) I would say the next following number is 20 (n + 1).
The nest number in the sequence is 18. Note that the difference between each number and the next number in the sequence follows the simple sequence of 1,2,3,4. Obviously the next in the sequence of increases is 5, so 13+5=18.
The next number in the sequence is 27.
Every next number is increased by 5. The next number in the sequence is 23.