3 x 17
No two prime numbers satisfy that request.
The prime factors of 51 are 3 and 17.
As a product of its prime factors: 3*17 = 51
3 and 17
3 and 17
17 and 3 are two prime numbers whose sum is 20. Their product is 51.
The two numbers are prime so their LCM is their product, which is 51.
31 is prime, but 51 is not as 51=3*17.
There are ten prime numbers between 51-100.
The digits in 51 add up to 6, so it is divisible by 3.51/3 = 17 (17, like 3 is a prime number)so the prime factors of 51 are the two numbers, 3 and 17(51, like all numbers, can also be divided without remainder by 1, but this is not usually counted as a prime factor)
51 + 29 = 80
51. The LCM of two prime numbers is their product. 3 x 17 = 51