Compare 661 vs 691
| Property | 661 | 691 |
|---|---|---|
| Type | prime | prime |
| Unique factors | 1 | 1 |
| Total factors | 1 | 1 |
| Prime factorization | 6611 | 6911 |
| Prime factorization | 661 | 691 |
| Divisors count | 2 | 2 |
| Divisors | 1, 661 | 1, 691 |
| Number of properties | 5 | 3 |
| Additive primes | 65th | |
| Centered decagonal primes | 8th | |
| Harmonic primes | 50th | |
| Isolated primes | 66th | |
| Primes | 121st | 125th |
| Pythagorean primes | 57th | |
| Twin primes (2nd member) | 30th | |
| Roman numberals | DCLXI | DCXCI |
| Base 2 | 10100101012 | 10101100112 |
| Base 3 | 2201113 | 2211213 |
| Base 4 | 221114 | 223034 |
| Base 5 | 101215 | 102315 |
| Base 6 | 30216 | 31116 |
| Base 7 | 16337 | 20057 |
| Base 8 | 12258 | 12638 |
| Base 9 | 8149 | 8479 |
| Base 10 | 66110 | 69110 |
| Base 11 | 55111 | 57911 |
| Base 12 | 47112 | 49712 |
| Base 13 | 3bb13 | 41213 |
| Base 14 | 35314 | 37514 |
| Base 15 | 2e115 | 31115 |
| Base 16 | 29516 | 2b316 |