2005 PMWC Problems/Problem T10
Problem
Find the largest 12-digit number for which every two consecutive digits form a distinct 2-digit prime number.
Solution
This page needs a solution. The original one, shown below, has an error (denoted by the bolded statement): the number is certainly not prime; it is divisible by 3.
Original Solution: We start with 97, which is the largest 2 digit prime.
97
Then we add 9 to get 79, the largest 2 digit prime with tens digit 7.
979
Add 3 to get 93, the largest prime less than 97
9793
Now the largest two digit prime with tens digit 3 is 37. So we add a 7
97937
Now we add another 3 as 79 already exists.
979373
And proceeding like this will get us
979373191713
See also
2005 PMWC (Problems) | ||
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