Compare 21 vs 28
| Property | 21 | 28 |
|---|---|---|
| Type | semiprime | composite number |
| Unique factors | 2 | 2 |
| Total factors | 2 | 3 |
| Prime factorization | 31 × 71 | 22 × 71 |
| Prime factorization | 3 × 7 | 2 × 2 × 7 |
| Divisors count | 4 | 6 |
| Divisors | 1, 3, 7, 21 | 1, 2, 4, 7, 14, 28 |
| Number of properties | 1 | 0 |
| Semiprimes | 7th | |
| Roman numberals | XXI | XXVIII |
| Base 2 | 101012 | 111002 |
| Base 3 | 2103 | 10013 |
| Base 4 | 1114 | 1304 |
| Base 5 | 415 | 1035 |
| Base 6 | 336 | 446 |
| Base 7 | 307 | 407 |
| Base 8 | 258 | 348 |
| Base 9 | 239 | 319 |
| Base 10 | 2110 | 2810 |
| Base 11 | 1a11 | 2611 |
| Base 12 | 1912 | 2412 |
| Base 13 | 1813 | 2213 |
| Base 14 | 1714 | 2014 |
| Base 15 | 1615 | 1d15 |
| Base 16 | 1516 | 1c16 |