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# 2-rough numbers

From OeisWiki

**2-rough numbers** could be interpreted in two ways:

- Positive integers that have no prime factors less than 2 (no primes are less than 2 since 1, a unit, is the empty product of primes), giving all the positive integers (see A000027

).( *n*),*n*≥ 1 - Positive integers whose smallest prime factor is 2, giving all the positive integers greater than 1 (see A000027

).( *n*),*n*≥ 2

## Positive integers that have no prime factors less than 2

Index_to_OEIS:_Section_Sk#smooth gives

smooth numbers, sequences related to : smooth numbers: k-rough numbers: k=2, A000027 ;

where A000027 are the positive integers

- {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, ...}