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A k-rough number, as defined by Finch in 2001 and 2003, is a positive integer whose prime factors are all greater than or equal to k. k-roughness has alternately been defined as requiring all prime factors to strictly exceed k.
Examples (after Finch)
- Every odd positive integer is 3-rough.
- Every positive integer that is congruent to 1 or 5 mod 6 is 5-rough.
- Every positive integer is 2-rough, since all its prime factors, being prime numbers, exceed 1.
References
Rough number Wikipedia(Text) CC BY-SA