Prime numbers to 50
The fifteen primes below fifty, marked on a grid of ten. This is the range to start on: small enough to check each number by hand, so what a prime is becomes obvious rather than memorized.
Reference chart
Prime numbers to 50
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
| 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 |
| 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 |
| 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 |
| 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48 | 49 | 50 |
What's on this chart
A prime has exactly two factors — one and itself — and nothing below fifty makes that easier to see. A child can test each square by asking what divides it evenly: 7 has only 1 and 7, so it is prime; 8 has 1, 2, 4, and 8, so it is not. Doing that a dozen times builds the idea far better than a definition does.
Why this chart helps
The pattern starts here too. After 2, every prime is odd; after 5, none end in 5. Point at the marked squares and a child sees the evens and the fives drop out, which is the first shortcut for spotting primes higher up.
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