In mathematics, a semiprime is a number that is the product of two not necessarily distinct primes. These integers are important in many contexts, including cryptography.
- is an example of a semiprime as it is the product of two threes. .
- is also an example as it is obtained by .
Other examples include: , , , , , and .
Examples of non-semiprimes
- , as it is only a prime number.
- , not a semiprime because it can obtained by or .
Via the Sieve of Sundaram formulation of: being composite any time , as , we can show that if and only if are both not composite producing then is a semiprime.
Odd semiprimes, are able to be expressed as a difference of squares, like all other numbers that are products of numbers of same parity.
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