The sequence is decreasing by a factor of 5 each time, so the next number would be -2.
The next number in the sequence is 18. It's +1, +2, +3, +4, ....
Every next number is increased by 5. The next number in the sequence is 23.
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.
18
20
The next number in the sequence would be 23. The sequence consists of prime numbers.
18
The sequence indicates that one number is added to the previous number to find the value of the next number. Example 1 (+0) - 1 (+1) - 2 (+1) - 3 (+2) - 5 (+3) - 8 (+5) - 13. The next number in the sequence would be 21 (13 + 8).
The next number would be 18. The sequence increases with +1, +2, +3... +5 etc. 13 + 5 = 18
21
If the last number is 1/3 (it should be), the next number is 5 and 1/3
42 is the next number in this sequence. This number sequence is adding the next prime number to the last number. So 1 + 2 = 3. Then 3 + 3 = 6, 6 + 5 = 11, 11 + 7 = 18, 18 + 11 = 29. The next prime number after 11 is 13, so 29 + 13 = 42. The next numbers would be 59 (42+17), 78 (59+19), and 101 (78+23)