Compare 21 vs 61
| Property | 21 | 61 |
|---|---|---|
| Type | semiprime | prime |
| Unique factors | 2 | 1 |
| Total factors | 2 | 1 |
| Prime factorization | 31 × 71 | 611 |
| Prime factorization | 3 × 7 | 61 |
| Divisors count | 4 | 2 |
| Divisors | 1, 3, 7, 21 | 1, 61 |
| Number of properties | 1 | 12 |
| Additive primes | 11th | |
| Centered decagonal primes | 3rd | |
| Centered square primes | 4th | |
| Cuban primes 1 | 4th | |
| Long primes | 8th | |
| Primes | 18th | |
| Pythagorean primes | 8th | |
| Semiprimes | 7th | |
| Sexy primes (1st member) | 12th | |
| Sexy prime quadrupletss (1st member) | 4th | |
| Sexy prime triplets (1st member) | 8th | |
| Solinas primes | 15th | |
| Twin primes (2nd member) | 7th | |
| Roman numberals | XXI | LXI |
| Base 2 | 101012 | 1111012 |
| Base 3 | 2103 | 20213 |
| Base 4 | 1114 | 3314 |
| Base 5 | 415 | 2215 |
| Base 6 | 336 | 1416 |
| Base 7 | 307 | 1157 |
| Base 8 | 258 | 758 |
| Base 9 | 239 | 679 |
| Base 10 | 2110 | 6110 |
| Base 11 | 1a11 | 5611 |
| Base 12 | 1912 | 5112 |
| Base 13 | 1813 | 4913 |
| Base 14 | 1714 | 4514 |
| Base 15 | 1615 | 4115 |
| Base 16 | 1516 | 3d16 |