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 A166061 19-rough numbers: positive integers that have no prime factors less than 19. 11
 1, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Or, positive integers relatively prime to 510510 = 2*3*5*7*11*13*17. LINKS Harvey P. Dale, Table of n, a(n) for n = 1..1000 Eric Weisstein's World of Mathematics, Rough Number Index entries for sequences related to smooth numbers [From Michael B. Porter, Oct 10 2009] FORMULA a(n) = k*n + O(1) where k = 17017/3072 = 5.539388.... In particular, k*n - 31 < a(n) < k*n + 25. - Charles R Greathouse IV, Sep 24 2018 EXAMPLE 437 = 19 * 23 is in the sequence since the two prime factors, 19 and 23, are not less than 19. MATHEMATICA Join[{1}, Select[Range[300], Min[Transpose[FactorInteger[#]][[1]]]>18&]] (* Harvey P. Dale, Feb 18 2015 *) PROG (PARI) isA166061(n) = gcd(n, 510510)==1 \\ Michael B. Porter, Oct 10 2009 CROSSREFS k-rough numbers: A000027, A005408, A007310, A007775, A008364, A008365, A008366, A166061, A166063. Sequence in context: A070299 A159021 A100460 * A224534 A073319 A274048 Adjacent sequences:  A166058 A166059 A166060 * A166062 A166063 A166064 KEYWORD easy,nonn AUTHOR Michael B. Porter, Oct 05 2009 STATUS approved

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Last modified September 30 14:57 EDT 2020. Contains 337439 sequences. (Running on oeis4.)