GCF Table 1–20
Greatest common factor for every pair of integers from 1 through 20.
| × | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 2 | 1 | 2 | 1 | 2 | 1 | 2 | 1 | 2 | 1 | 2 | 1 | 2 | 1 | 2 | 1 | 2 | 1 | 2 | 1 | 2 |
| 3 | 1 | 1 | 3 | 1 | 1 | 3 | 1 | 1 | 3 | 1 | 1 | 3 | 1 | 1 | 3 | 1 | 1 | 3 | 1 | 1 |
| 4 | 1 | 2 | 1 | 4 | 1 | 2 | 1 | 4 | 1 | 2 | 1 | 4 | 1 | 2 | 1 | 4 | 1 | 2 | 1 | 4 |
| 5 | 1 | 1 | 1 | 1 | 5 | 1 | 1 | 1 | 1 | 5 | 1 | 1 | 1 | 1 | 5 | 1 | 1 | 1 | 1 | 5 |
| 6 | 1 | 2 | 3 | 2 | 1 | 6 | 1 | 2 | 3 | 2 | 1 | 6 | 1 | 2 | 3 | 2 | 1 | 6 | 1 | 2 |
| 7 | 1 | 1 | 1 | 1 | 1 | 1 | 7 | 1 | 1 | 1 | 1 | 1 | 1 | 7 | 1 | 1 | 1 | 1 | 1 | 1 |
| 8 | 1 | 2 | 1 | 4 | 1 | 2 | 1 | 8 | 1 | 2 | 1 | 4 | 1 | 2 | 1 | 8 | 1 | 2 | 1 | 4 |
| 9 | 1 | 1 | 3 | 1 | 1 | 3 | 1 | 1 | 9 | 1 | 1 | 3 | 1 | 1 | 3 | 1 | 1 | 9 | 1 | 1 |
| 10 | 1 | 2 | 1 | 2 | 5 | 2 | 1 | 2 | 1 | 10 | 1 | 2 | 1 | 2 | 5 | 2 | 1 | 2 | 1 | 10 |
| 11 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 11 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 12 | 1 | 2 | 3 | 4 | 1 | 6 | 1 | 4 | 3 | 2 | 1 | 12 | 1 | 2 | 3 | 4 | 1 | 6 | 1 | 4 |
| 13 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 13 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| 14 | 1 | 2 | 1 | 2 | 1 | 2 | 7 | 2 | 1 | 2 | 1 | 2 | 1 | 14 | 1 | 2 | 1 | 2 | 1 | 2 |
| 15 | 1 | 1 | 3 | 1 | 5 | 3 | 1 | 1 | 3 | 5 | 1 | 3 | 1 | 1 | 15 | 1 | 1 | 3 | 1 | 5 |
| 16 | 1 | 2 | 1 | 4 | 1 | 2 | 1 | 8 | 1 | 2 | 1 | 4 | 1 | 2 | 1 | 16 | 1 | 2 | 1 | 4 |
| 17 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 17 | 1 | 1 | 1 |
| 18 | 1 | 2 | 3 | 2 | 1 | 6 | 1 | 2 | 9 | 2 | 1 | 6 | 1 | 2 | 3 | 2 | 1 | 18 | 1 | 2 |
| 19 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 19 | 1 |
| 20 | 1 | 2 | 1 | 4 | 5 | 2 | 1 | 4 | 1 | 10 | 1 | 4 | 1 | 2 | 5 | 4 | 1 | 2 | 1 | 20 |
How to use this table
Greatest common factor for every pair of integers from 1 through 20. Use it as a reference, for practice, or to check your own work. On large tables, scroll horizontally on a phone. Tap cells to visually track a row or value.