A sphenic number is a positive integer that is the product of three distinct prime factors. The Möbius function returns when passed any sphenic number.

Note that this definition is more stringent than simply requiring the integer to have exactly three prime factors; e.g. 60 = 2² × 3 × 5 has exactly 3 prime factors, but is not sphenic.

All sphenic numbers have exactly eight divisors. If we express the sphenic number as , then its divisors will be (possibly not sorted):

The first few sphenic numbers are: 30, 42, 66, 70, 78, 102, 105, 110, 114, 130, ...

External links

• Sphenic numbers from On-Line Encyclopedia of Integer Sequences.