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A038509
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Composite numbers congruent to +-1 mod 6.
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36
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25, 35, 49, 55, 65, 77, 85, 91, 95, 115, 119, 121, 125, 133, 143, 145, 155, 161, 169, 175, 185, 187, 203, 205, 209, 215, 217, 221, 235, 245, 247, 253, 259, 265, 275, 287, 289, 295, 299, 301, 305, 319, 323, 325, 329, 335, 341, 343, 355, 361, 365, 371, 377, 385
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Or, composite numbers with smallest prime factor >= 5.
Or, nonprime numbers n such that binomial(n+3, 3) mod n == 1. - Hieronymus Fischer (Hieronymus.Fischer(AT)gmx.de), Sep 30 2007
Note that the primes > 3 are congruent to +-1 mod 6.
This sequence differs from A067793 (composite n such that phi(n) > 2n/3) starting at 385. Numbers in this sequence but not in A067793 are 385, 455, 595, 665, 805, 1015, 1085, 1925, 2275, 2695, etc. See A069043. - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jun 08 2008 and Moshe Levin, Nov 02 2011.
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MATHEMATICA
| Select[Range[1000], FactorInteger[#][[1, 1]] >= 5 && ! PrimeQ[#] &] [From Robert G. Wilson v (rgwv(AT)rgwv.com), Dec 19 2009]
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CROSSREFS
| Cf. A171993 (nonprimes of the form 3*k+-1).
Cf. A000040, A133620-A133625, A133630, A133634-A133636.
Cf. A133873, A133883, A133880, A133890, A133900, A133910.
Cf. A069043, A067793 (composite n such that phi(n) > 2n/3).
Sequence in context: A049518 A133633 A067793 * A054550 A107472 A193165
Adjacent sequences: A038506 A038507 A038508 * A038510 A038511 A038512
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KEYWORD
| nonn,nice
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AUTHOR
| Jeff Burch (gburch(AT)erols.com)
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EXTENSIONS
| More terms from Robert G. Wilson v (rgwv(AT)rgwv.com), Dec 19 2009
Entry revised by N. J. A. Sloane, Dec 31 2011, at the suggestion of Gary Detlefs.
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