What is then next number in the sequence?

2, 3, 5, 7, 11, 13, 17, 19, 23, _

To find the next number in the sequence, let's analyze the pattern.

This sequence appears to be a list of prime numbers in ascending order:

2, 3, 5, 7, 11, 13, 17, 19, 23, _

Therefore, the next prime number after 23 is 29.

So, the next number in the sequence is 29.