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A008366 Smallest prime factor is >= 17. 11
1, 17, 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, 277, 281, 283 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Also the 17-rough numbers: positive integers that have no prime factors less than 17. - Michael B. Porter, Oct 10 2009

a(n) - (1001/192) n is periodic with period 5760. - Robert Israel, Mar 18 2016

From Peter Bala, May 12 2018: (Start)

The product of two 17-rough numbers is a 17-rough number and the prime factors of a 17-rough number are 17-rough numbers.

Let k equal either 13, 14, 15 or 16. Then the product of k numbers n*(n + a)*(n + 2*a)*...*(n + (k-1)*a) in arithmetical progression is divisible by k! for all integer n if and only if a is a 17-rough number.

The sequence terms satisfy the congruence x^60 = 1 (mod 30030), where 30030 = 2*3*5*7*11*13. (End)

The asymptotic density of this sequence is 192/1001. - Amiram Eldar, Sep 30 2020

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

Peter Bala, A property of p-rough numbers.

Benedict Irwin, Generating Function.

Eric Weisstein's World of Mathematics, Rough Number.

Index entries for sequences related to smooth numbers [Michael B. Porter, Oct 10 2009]

FORMULA

Numbers n > 1 such that ((Sum_{k=1..n} k^10) mod n = 0) and ((Sum_{k=1..n} k^12) mod n = 0) (conjecture). - Gary Detlefs, Dec 27 2011

a(n) = a(n-1) + a(n-5760) - a(n-5761). - Vaclav Kotesovec, Mar 18 2016

G.f: x*P(x)/(1 - x - x^5760 + x^5761) where P(x) is a polynomial of degree 5760. - Benedict W. J. Irwin, Mar 23 2016

MAPLE

for i from 1 to 500 do if gcd(i, 30030) = 1 then print(i); fi; od;

MATHEMATICA

Select[ Range[ 300 ], GCD[ #1, 30030 ]==1& ]

Join[{1}, Select[Range[300], FactorInteger[#][[1, 1]]>=17&]] (* Harvey P. Dale, Mar 28 2020 *)

PROG

(PARI) isA008366(n) = gcd(n, 30030)==1 \\ Michael B. Porter, Oct 10 2009

CROSSREFS

For k-rough numbers with other values of k, see A000027 A005408 A007310 A007775 A008364 A008365 A008366 A166061 A166063. - Michael B. Porter, Oct 10 2009

Cf. A005867.

Sequence in context: A054484 A054796 A322275 * A126769 A092216 A180948

Adjacent sequences:  A008363 A008364 A008365 * A008367 A008368 A008369

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane

STATUS

approved

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Last modified November 28 02:22 EST 2020. Contains 338699 sequences. (Running on oeis4.)