GCF for 7, 15 and 21
"Greatest Common Factor of 3 Numbers" Calculator
What's the Greatest Common Factor (GCF) of 7, 15 and 21?
Answer
GCF of 7, 15 and 21 is
1
Common factors: 1
Only 1 divides all three: no prime is a factor of each of 7, 15 and 21.
Pairs do share factors — GCF(7, 21) = 7, GCF(15, 21) = 3 — just none greater than 1 common to all three.
7 — prime
15 = 3 × 5
21 = 3 × 7
| Prime | 7 | 15 | 21 | Lowest power |
|---|---|---|---|---|
| 3 | — | 3 | 3 | — |
| 5 | — | 5 | — | — |
| 7 | 7 | — | 7 | — |
— = power 0: the prime is not a factor of this number, so it cannot be in the GCF.
GCF = 1
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See Also
- Least Common Multiple of 3 Numbers - Find the Least Common Multiple (LCM) of three numbers
- Greatest Common Factor - Find the Greatest Common Factor (GCF) of two numbers
- Least Common Multiple - Find the Least Common Multiple (LCM) of two numbers
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GCF Table
| 1st | 2nd | 3rd | GCF |
|---|---|---|---|
| 6 | 7 | 15 | 1 |
| 7 | 7 | 15 | 1 |
| 7 | 8 | 15 | 1 |
| 7 | 9 | 15 | 1 |
| 7 | 10 | 15 | 1 |
| 7 | 11 | 15 | 1 |
| 7 | 12 | 15 | 1 |
| 7 | 13 | 15 | 1 |
| 7 | 14 | 15 | 1 |
| 7 | 15 | 15 | 1 |
| 7 | 15 | 16 | 1 |
| 7 | 15 | 17 | 1 |
| 7 | 15 | 18 | 1 |
| 7 | 15 | 19 | 1 |
| 7 | 15 | 20 | 1 |
| 7 | 15 | 21 | 1 |
| 7 | 15 | 22 | 1 |
| 7 | 15 | 23 | 1 |
| 7 | 15 | 24 | 1 |
| 7 | 15 | 25 | 1 |
| 7 | 15 | 26 | 1 |
| 7 | 15 | 27 | 1 |
| 7 | 15 | 28 | 1 |
| 7 | 15 | 29 | 1 |
| 7 | 15 | 30 | 1 |
| 7 | 15 | 31 | 1 |
| 7 | 15 | 32 | 1 |
| 7 | 15 | 33 | 1 |
| 7 | 15 | 34 | 1 |
| 7 | 15 | 35 | 1 |