Compare 21 vs 37
| Property | 21 | 37 |
|---|---|---|
| Type | semiprime | prime |
| Unique factors | 2 | 1 |
| Total factors | 2 | 1 |
| Prime factorization | 31 × 71 | 371 |
| Prime factorization | 3 × 7 | 37 |
| Divisors count | 4 | 2 |
| Divisors | 1, 3, 7, 21 | 1, 37 |
| Number of properties | 1 | 18 |
| Chen primes | 12th | |
| Cousin primes (1st member) | 5th | |
| Cuban primes 1 | 3rd | |
| Emirps | 4th | |
| Good primes | 5th | |
| Isolated primes | 3rd | |
| Left-truncatable primes | 8th | |
| Lucky primes | 5th | |
| Pierpont primes | 8th | |
| Primes | 12th | |
| Prime triplets (1st member) | 6th | |
| Pythagorean primes | 5th | |
| Right-truncatable primes | 8th | |
| Semiprimes | 7th | |
| Sexy primes (1st member) | 8th | |
| Sexy primes (2nd member) | 7th | |
| Sexy prime triplets (2nd member) | 5th | |
| Solinas primes | 11th | |
| Two-sided primes | 6th | |
| Roman numberals | XXI | XXXVII |
| Base 2 | 101012 | 1001012 |
| Base 3 | 2103 | 11013 |
| Base 4 | 1114 | 2114 |
| Base 5 | 415 | 1225 |
| Base 6 | 336 | 1016 |
| Base 7 | 307 | 527 |
| Base 8 | 258 | 458 |
| Base 9 | 239 | 419 |
| Base 10 | 2110 | 3710 |
| Base 11 | 1a11 | 3411 |
| Base 12 | 1912 | 3112 |
| Base 13 | 1813 | 2b13 |
| Base 14 | 1714 | 2914 |
| Base 15 | 1615 | 2715 |
| Base 16 | 1516 | 2516 |