Semi-prime
Definition
Two product of prime numbers is called a Semiprime.
Description
Examples of semiprimes include , , , etc.
In Japanese translation, it is also called 半素数 but it is hard to find either semiprime or 半素数 in the Korean documents.
Essentially, semiprime is not a semiprime itself, but it somewhat inherits the properties of prime numbers and is applied. For example, if you make a semiprime by multiplying two rather large prime numbers, its prime factorization is quite difficult. The difficulty of this prime factorization problem is exactly what the RSA cryptosystem uses.