Properties
The total number of prime factors Ω(n) for a semiprime n is two, by definition. A semiprime is either a square of a prime or square-free.
For a semiprime n = pq the value of Euler's totient function (the number of positive integers less than or equal to n that are relatively prime to n) is particularly simple when p and q are distinct:
- φ(n) = (p − 1) (q − 1) = p q − (p + q) + 1 = n − (p + q) + 1.
If otherwise p and q are the same,
- φ(n) = φ(p2) = (p − 1) p = p2 − p = n − p.
The concept of the prime zeta function can be adapted to semiprimes, which defines constants like
- (sequence A117543 in OEIS)
- (sequence A152447 in OEIS)
- (sequence A154928 in OEIS)
Read more about this topic: Semiprime
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—Ralph Waldo Emerson (1803–1882)
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