Compare 21 vs 47
| Property | 21 | 47 |
|---|---|---|
| Type | semiprime | prime |
| Unique factors | 2 | 1 |
| Total factors | 2 | 1 |
| Prime factorization | 31 × 71 | 471 |
| Prime factorization | 3 × 7 | 47 |
| Divisors count | 4 | 2 |
| Divisors | 1, 3, 7, 21 | 1, 47 |
| Number of properties | 1 | 21 |
| Additive primes | 10th | |
| Carol primes | 2nd | |
| Chen primes | 14th | |
| Class 1+ primes | 9th | |
| Cousin primes (2nd member) | 6th | |
| Isolated primes | 4th | |
| Left-truncatable primes | 10th | |
| Long primes | 6th | |
| Lucas primes | 6th | |
| Pierpont primes of the 2nd kind | 9th | |
| Primes | 15th | |
| Prime triplets (3rd member) | 7th | |
| Safe primes | 5th | |
| Semiprimes | 7th | |
| Sexy primes (1st member) | 10th | |
| Sexy primes (2nd member) | 9th | |
| Sexy prime quadrupletss (2nd member) | 3rd | |
| Sexy prime triplets (1st member) | 7th | |
| Sexy prime triplets (2nd member) | 6th | |
| Solinas primes | 13th | |
| Thabit primes | 5th | |
| Ulam primes | 5th | |
| Roman numberals | XXI | XLVII |
| Base 2 | 101012 | 1011112 |
| Base 3 | 2103 | 12023 |
| Base 4 | 1114 | 2334 |
| Base 5 | 415 | 1425 |
| Base 6 | 336 | 1156 |
| Base 7 | 307 | 657 |
| Base 8 | 258 | 578 |
| Base 9 | 239 | 529 |
| Base 10 | 2110 | 4710 |
| Base 11 | 1a11 | 4311 |
| Base 12 | 1912 | 3b12 |
| Base 13 | 1813 | 3813 |
| Base 14 | 1714 | 3514 |
| Base 15 | 1615 | 3215 |
| Base 16 | 1516 | 2f16 |