23
23 is the smallest prime number greater than 20.
The prime number that is greater than 20 but less than 29 is 23.
23
20 is the next number greater than 19. The next prime number greater than 19 is 23.
31.
23
There are many greater than 20, a better questions would've been "what prime numbers are less than 20". The first prime number greater than 20 is 23. The prime numbers to 100 are 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97
21 = 3x7 ... not prime. 22 = 2x11 ... not prime. 23 is prime. 23.
23 and 29 are the prime numbers between 20 and 30.
25 is the number not less than 20, not greater than 40, not divisible by 2 3 or 7, and not a prime number.
23 and 29
23^2=529