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Proth numbers

A Proth number has the form k * 2^n + 1, where k is positive and odd, n >= 1, and k < 2^n. It need not be prime.

The first few proth numbers are: 3, 5, 9, 13, 17, 25, 33, 41, 49, 57, 65, 81, …

1,487 of the first one million positive integers are proth.

Learn more about proth numbers on wikipedia.

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