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Sphenic number

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Sphenic numbers are numbers that are the product of three distinct prime numbers. For example, 42 is a sphenic number since . See A007304 for more sphenic numbers.

Sphenic numbers have precisely 8 divisors, namely: 1, the three distinct primes, three semiprimes (in which each of the distinct prime factors of the sphenic number is omitted) and the sphenic number itself; e.g. for 42: 1, 2, 3, 7, 21 (equals 3 times 7, 2 is omitted), 14 (equals 2 times 7, 3 is omitted), 6 (equals 2 times 3, 7 is omitted) and 42 itself. (The product of the cube of a prime and another prime as well as seventh powers of primes also have 8 divisors).