Singly even numbers

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Singly even numbers are integers divisible by 2 but not by 4 nor by any larger power of 2. The first few are 2, 6, 10, 14, 18, 22, 26, 30, 34, 38, 42, 46 (see A016825).

These numbers have as many even divisors as they have odd divisors.

The fraction of singly even numbers which are squarefree is $8/\pi ^{2}$ or about 81%. No singly even number can be a perfect square.