Thinking 1 is a prime number
"The One Error"
The Mistake in Action
List all the prime factors of 30.
Wrong: 1, 2, 3, 5
Why It Happens
Students remember that primes "only divide by 1 and themselves" and incorrectly include 1.
The Fix
A prime number has exactly two factors: 1 and itself.
The number 1 only has one factor (itself), so it is NOT prime.
Prime factors of 30: 2, 3, 5 (not 1!)
$$30 = 2 \times 3 \times 5$$
Key primes to know: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29...
Spot the Mistake
Can you identify where this student went wrong?
List all prime factors of 30
1, 2, 3, 5
Click on the line that contains the error.
Related Topics
Learn more about the underlying maths: