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A053181
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Composite numbers ending in 9.
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2
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9, 39, 49, 69, 99, 119, 129, 159, 169, 189, 209, 219, 249, 259, 279, 289, 299, 309, 319, 329, 339, 369, 399, 429, 459, 469, 489, 519, 529, 539, 549, 559, 579, 589, 609, 629, 639, 649, 669, 679, 689, 699, 729, 749, 759, 779, 789, 799, 819, 849, 869, 879, 889, 899
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OFFSET
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1,1
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COMMENTS
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Numbers of the form 10n + 9 (A017377) not in A030433. Obviously multiples of 2 or 5 can't be in A017377 nor this sequence. All other primes occur as factors of these terms infinitely often. For example: If n is a multiple of 3, then 10n + 9 is in this sequence; if n = 4 mod 7, then 10n + 9 is in this sequence; if n = 9 mod 11, then 10n + 9 is in this sequence; and so on and so forth. The first of these congruences to be satisfied determines the least prime factor of 10n + 9. - Alonso del Arte, Jun 23 2011
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LINKS
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FORMULA
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MATHEMATICA
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Complement[Range[9, 1000, 10], Prime[Range[PrimePi[1000]]]] (* Alonso del Arte, Jun 23 2011 *)
Select[Range[1000], CompositeQ[#]&&Mod[#, 10]==9&] (* Harvey P. Dale, May 01 2016 *)
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PROG
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CROSSREFS
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KEYWORD
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easy,nonn,base
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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