15
17?
The next number is 4. 1, 3, 2, 5, 7, 4, 9, 11, 6
41
7 followed by 43, 9, 52, 11, and 63 etc.
The next number in this sequence is 13112221.
it has to be 11
11
71422315
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)
The next number in the sequence would be 23. The sequence consists of prime numbers.
It all depends on the sequence you are talking about. For example, the next number in the sequence 0,1,1,2,3,5,8,13,_ would be 21. This would be the Fibonacci sequence as the rule is add the 2 previous terms to get the next term. Another example would be this: 11,121,1331,14641,______.The missing number is 161051, following the pattern of powers of 11, 11^1, 11^2, 11^3 and so on. If you understand what I am trying to say, it all depends on the sequence you are trying to find the number in.