It's good to be able to recognize all the
prime numbers less than 100:

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.

Those greater than 20 are

23, 29, 31, 37, 41, 43, 47, 53, 59,
61, 67, 71, 73, 79, 83, 89, 97.

The only one that has sum of digits 4 is 31, since 3+1=4.

31 is greater than 20.

The product of its digits is 3×1 = 3, which is less than 5

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All the two-digit prime numbers less than 20 are

11, 13, 17, 19

The only one with sum of digits 4 is 13, since 1+3=4. 

Its product of digits is 1×3 = 3, which is less than 5.

Edwin