The number 17,31 and 73 are prime numbers reversing the order of the digits to make 71,13 and 37 are also result in prime numbers does reversing the order of the digits of a two digit prime number always result in a prime number explain
take the example of 19. it is a prime number but when flipped gives 91, divisible by 7 and 13, therefore not prime. The examples in the question were just carefully selected to be true.
