Sphenic number

A sphenic number is a number that has precisely three distinct prime factors. The Möbius function returns -1 when passed any sphenic number.

All sphenic numbers have exactly eight divisors. If we express the sphenic number as n = p_xp_yp_z, then its divisors will be {1, p_x, p_y, p_z, p_xp_y, p_xp_z, p_yp_z, n} (though this might not always result in a list sorted from lowest to highest).

The first ten sphenic numbers are:

1. 30
2. 42
3. 66
4. 70
5. 78
6. 102
7. 105
8. 110
9. 114
10. 130

See also

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