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Problem of the Week 1218

A Prime-Sum Circle

Arrange the numbers 1, 2, 3, ..., 20 in a circle so that the sum of any two neighboring numbers is prime.

Extra Credit. Resolve this with 20 replaced by n.

Source: Inspired by G. Hamilton, K.S. Kedlaya, and H. Picciotto, Square-sum pair partitions, College Math. Journal 46 (Sept. 2015) 264-269, but original with me in this prime version.

[View the solution]

January 2016