Compare 18 vs 21
| Property | 18 | 21 |
|---|---|---|
| Type | composite number | semiprime |
| Unique factors | 2 | 2 |
| Total factors | 3 | 2 |
| Prime factorization | 21 × 32 | 31 × 71 |
| Prime factorization | 2 × 3 × 3 | 3 × 7 |
| Divisors count | 6 | 4 |
| Divisors | 1, 2, 3, 6, 9, 18 | 1, 3, 7, 21 |
| Number of properties | 0 | 1 |
| Semiprimes | 7th | |
| Roman numberals | XVIII | XXI |
| Base 2 | 100102 | 101012 |
| Base 3 | 2003 | 2103 |
| Base 4 | 1024 | 1114 |
| Base 5 | 335 | 415 |
| Base 6 | 306 | 336 |
| Base 7 | 247 | 307 |
| Base 8 | 228 | 258 |
| Base 9 | 209 | 239 |
| Base 10 | 1810 | 2110 |
| Base 11 | 1711 | 1a11 |
| Base 12 | 1612 | 1912 |
| Base 13 | 1513 | 1813 |
| Base 14 | 1414 | 1714 |
| Base 15 | 1315 | 1615 |
| Base 16 | 1216 | 1516 |