Peter has 25 cards, each printed with a different integer from 1 to 25. He wishes to place cards in a single row so that the numbers on every adjacent pair of cards have a prime factor in common.
What is the largest value of for which this is possible?
Select one option, then click Submit.
16
18
20
22
24
Select an option, then submit.
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Senior Mathematical Challenge 2015 (2015)
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