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Using all the single digits once only, and excluding 0, what's the minumum sum you can make when the numbers to be added are all prime?
In base 5, for example, we have the digits 1, 2, 3 and 4; two possible answers are:
12 + 34 = 101 and 14 + 32 = 101
and in base ten 2 + 3 + 5 +47 + 61 + 89 = 207 is the minimum sum (I'm told - I didn't work it out).
At the moment I have the following results for
| Base six | 3 + 21 + 45 = 113 |
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| Base seven | 2 + 5 + 43 + 61 = 144 |
| Base eight | 2 + 3 + 65 + 417 = 511 |
any more?