Compare 661 vs 665
| Property | 661 | 665 |
|---|---|---|
| Type | prime | composite number |
| Unique factors | 1 | 3 |
| Total factors | 1 | 3 |
| Prime factorization | 6611 | 51 × 71 × 191 |
| Prime factorization | 661 | 5 × 7 × 19 |
| Divisors count | 2 | 8 |
| Divisors | 1, 661 | 1, 5, 7, 19, 35, 95, 133, 665 |
| Number of properties | 5 | 0 |
| Additive primes | 65th | |
| Centered decagonal primes | 8th | |
| Primes | 121st | |
| Pythagorean primes | 57th | |
| Twin primes (2nd member) | 30th | |
| Roman numberals | DCLXI | DCLXV |
| Base 2 | 10100101012 | 10100110012 |
| Base 3 | 2201113 | 2201223 |
| Base 4 | 221114 | 221214 |
| Base 5 | 101215 | 101305 |
| Base 6 | 30216 | 30256 |
| Base 7 | 16337 | 16407 |
| Base 8 | 12258 | 12318 |
| Base 9 | 8149 | 8189 |
| Base 10 | 66110 | 66510 |
| Base 11 | 55111 | 55511 |
| Base 12 | 47112 | 47512 |
| Base 13 | 3bb13 | 3c213 |
| Base 14 | 35314 | 35714 |
| Base 15 | 2e115 | 2e515 |
| Base 16 | 29516 | 29916 |