Ponder This Challenge - February 2026 - Blot-avoiding backgammon strategy
- Ponder This
Forming primes in digit circles
The following riddle was suggested by Evert van Dijken.
Seven distinct digits are places on a circle. Then, numbers can be formed in the following manner: Choose one digit to start from and add it to the number, and then move a certain number of steps on the circle either clockwise or counterclockwise. Add the digit to the number, and keep this until five digits were chosen. These digits comprise the number (the first digit being the most significant digit).
For example, in the circle [4, 7, 3, 6, 2, 0, 1]:
One can start from "2", move 3 steps clockwise to "4", move one step counterclockwise to "1", move one more step counterclockwise to "0", and move 4 steps clockwise to "3", resulting in the number "24103".
Given a circle, we assign a score to each number that can be generated from the circle based on the minimum number of steps required to generate this number. In the example above, moving from "0" to "3" in 4 steps is not optimal; one can move just 3 steps by going counterclockwise. So the score of "24103" is 3+1+1+3=8.
We allow generation only of the numbers that satisfy all the following criterions:
For a given circle, we can form all the numbers that satisfy the criterion and sum their scores.
For the circle [4, 7, 3, 6, 2, 0, 1] we will find 231 total primes with 5 distinct digits, giving us a total score of 1882. This 1882 is the score of the circle itself.
In our example we had digits in a circle and the numbers had digits but we can also generalize for different values of (if , we can use a different number base, but we won't do it here).
Your goal: Find circles giving the maximum and minimum score for the original setting.
Send your result in the following format:
[a1, a2, ..., an]
[b1, b2, ..., bn]
A bonus "*" will be given for finding circles giving the maximum and minimum score for .
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For the maximum score is 3051 and the minimum is 446.
A pair of circles giving those values is [4, 5, 2, 1, 7, 3, 9] ,[1, 0, 6, 2, 8, 5, 4]
For the maximum score is 23209 and the minimum is 8265.
A pair of circles giving those values is [0, 1, 4, 8, 2, 5, 9, 6], [1,8,2,3,4,6,7,9]