Compare 21 vs 53
| Property | 21 | 53 |
|---|---|---|
| Type | semiprime | prime |
| Unique factors | 2 | 1 |
| Total factors | 2 | 1 |
| Prime factorization | 31 × 71 | 531 |
| Prime factorization | 3 × 7 | 53 |
| Divisors count | 4 | 2 |
| Divisors | 1, 3, 7, 21 | 1, 53 |
| Number of properties | 1 | 18 |
| Chen primes | 15th | |
| Class 1+ primes | 10th | |
| Good primes | 7th | |
| Isolated primes | 5th | |
| Left-truncatable primes | 11th | |
| Pierpont primes of the 2nd kind | 10th | |
| Primes | 16th | |
| Pythagorean primes | 7th | |
| Restricted right-truncatable primes | 1st | |
| Right-truncatable primes | 9th | |
| Semiprimes | 7th | |
| Sexy primes (1st member) | 11th | |
| Sexy primes (2nd member) | 10th | |
| Sexy prime quadrupletss (3rd member) | 3rd | |
| Sexy prime triplets (2nd member) | 7th | |
| Sexy prime triplets (3rd member) | 6th | |
| Sophie germain primes | 8th | |
| Two-sided primes | 7th | |
| Ulam primes | 6th | |
| Roman numberals | XXI | LIII |
| Base 2 | 101012 | 1101012 |
| Base 3 | 2103 | 12223 |
| Base 4 | 1114 | 3114 |
| Base 5 | 415 | 2035 |
| Base 6 | 336 | 1256 |
| Base 7 | 307 | 1047 |
| Base 8 | 258 | 658 |
| Base 9 | 239 | 589 |
| Base 10 | 2110 | 5310 |
| Base 11 | 1a11 | 4911 |
| Base 12 | 1912 | 4512 |
| Base 13 | 1813 | 4113 |
| Base 14 | 1714 | 3b14 |
| Base 15 | 1615 | 3815 |
| Base 16 | 1516 | 3516 |