One possible answer is 2, 3, 5, 41, 67, 89
Another possible answer is 2, 3, 5, 47, 61, 89
Other answers may be possible.
=============================================================
Explanation:
This is a trial and error type of problem. Though with practice it's not as blind of randomly guessing.
We have 9 values here. If we paired them up, then we can form at most 4 pairs (since 9/2 = 4.5 rounds down to 4). That means we won't be able to form six two-digit primes. Some of the primes must be single digits.
We can have 3 single digit primes and 3 two-digit primes since 3+2*3 = 9.
The single digit primes are: 2, 3, 5, 7
Let's say 2 and 5 are definitely locked down to be the single digit group. I'm doing this since we can't have 2 or 5 as the units digit. If the units digit is 2, then 2 is a factor and it's not prime. Similarly, if 5 is the units digit, then 5 is a factor and that two digit value is not prime.
For good measure, we'll throw 3 in there as well and see what happens.
------------------
The digits we have left are: 1, 4, 6, 7, 8, 9
The number 14 isn't prime, but 41 is prime
67 is prime so that's another two values off the list
lastly, 89 is prime so that works as well.
So one possible sequence is 2, 3, 5, 41, 67, 89
Notice how we can swap the 1 and 7 to go from 41,67 to 47,61; this gets us two other primes. So another possible answer is 2, 3, 5, 47, 61, 89
------------------
Side note: having the list of primes on a reference sheet is a handy recommendation. You only need to go up as high as 97 which is the largest two digit prime.
