ERJ Brainteaser - September
1 Sep 2026
Each month, ERJ sets a weekly brainteaser, with questions of varying degrees of difficulty. Readers supplying the most accurate (and stylish) answers are then considered for the prestigious Brainiac of the Month title
Question 1: Secret combination
For maximum security, Sara has purchased two combination locks for her bicycle, each having a five-digit code. When choosing the codes, she decided to use the smallest and largest numbers that met the following conditions:
- Each digit of the number was a prime digit.
- Each successive pair of digits formed a two-digit number that was not a prime number.
- Each of the prime digits had to appear at least once in the five-digit number.
What were the codes for Sara’s combination locks?
Email your answer: correct replies on Friday.
