I am a three-digit prime number. My middle digit is zero. My first and last digits are consecutive numbers, and my first digit is smaller than my last digit. What number am I?
103
The digits are 1, 0, 3. The middle is 0. The first (1) and last (3) are not consecutive. Wait, consecutive means in a row like 1, 2 or 2, 3. Let's look at 203: 2 and 3 are consecutive, 2 < 3. Is 203 prime? 203 = 7 x 29, so no. What about 103? 1 and 3 are not consecutive. What about 304? Not prime. Let's look for consecutive digits where first < last, middle is 0, and it's prime. How about 405? Ends in 5, not prime. 506? Even, not prime. 607? 6 and 7 are consecutive, middle is 0, 607 is prime! Let's check: 6, 0, 7. First is 6, last is 7 (consecutive, 6 < 3? No, 6 < 7). Middle is 0. 607 has no positive divisors other than 1 and itself.
About this riddle
Math riddles hide a calculation inside a short story. Pull out the numbers, work out what is being asked, and watch for a trick such as a unit change.
Difficulty: Hard. More like this: Math riddles with answers or try Target 24 for a different kind of puzzle.
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