Solution of the Week #578 - Prime Bridge

It is tempting to think that the number 2 should be the designated driver for the whole endeavour:

2,3,5

2

2,7,11

2

2,13,17

2

2,19,23

which would take a total of 62 minutes. However we can get it under an hour:

2,3,5

2

7,11,13

3

17,19,23

5

2,3,5

which takes just 56 minutes.

But even this isn’t optimal. If we combine the two methods we can shave another minute off:

2,3,7

2

2,11,13

2

17,19,23

3

2,3,5

Giving a total of 55 minutes.