That's an infinite list. 1.287465, 1.25, 1.22222...
If by between you mean strictly between (that is, not including either 12 or 40), the answer is 13.
12.1 12.2
It is: 12 and 13
13 17 19 23 29 31.
12. 13, if you count 200
There are an infinite number of numbers between 12 and 13. decimals, fractions and irrational numbers
prime numbers between 12 and18: 13, & 17
13
12
The square numbers between 10 and 40 are 16,25 and 36.
If by between you mean strictly between (that is, not including either 12 or 40), the answer is 13.
The square root of 150 is between 12 and 13.
12.1 12.2
13 and 22
It is: 12 and 13
13 17 19 23
13, 15, 17 and 19