A sphenic number is the product of exactly three distinct prime numbers, each appearing to the first power. The name comes from the Greek sphenos ("wedge"), reflecting the geometric idea of three primes "wedged" together.
The first sphenic numbers are 30 = 2·3·5, 42 = 2·3·7, 66 = 2·3·11, 70 = 2·5·7, 78 = 2·3·13, 102 = 2·3·17.
Every sphenic number has exactly 8 divisors (1, the three primes, the three pairwise products, and the number itself), and is automatically squarefree. Sphenic numbers are a special case of squarefree numbers with exactly three prime factors.