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A157483
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Numbers n such that n-+1 are divisible by exactly 3 primes, counted with multiplicity.
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6
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19, 29, 43, 51, 67, 69, 77, 115, 171, 173, 187, 189, 237, 243, 245, 267, 274, 283, 285, 291, 317, 344, 355, 386, 403, 405, 411, 424, 427, 429, 435, 437, 476, 507, 597, 603, 604, 605, 638, 653, 664, 669, 723, 763, 776, 787, 789, 846, 891, 893, 907, 926, 963
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| 18=2*3*3,20=2*2*5, ...
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MAPLE
| with(numtheory); a := proc (n) if bigomega(n-1) = 3 and bigomega(n+1) = 3 then n else end if end proc: seq(a(n), n = 2 .. 1100); [From Emeric Deutsch (deutsch(AT)duke.poly.edu), Mar 03 2009]
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MATHEMATICA
| q=3; lst={}; Do[If[Plus@@Last/@FactorInteger[n-1]==q&&Plus@@Last/@FactorInteger[n+1]==q, AppendTo[lst, n]], {n, 7!}]; lst
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CROSSREFS
| Cf. A124936, A014612, A156028
Sequence in context: A158846 A157026 A108183 * A173966 A096218 A100590
Adjacent sequences: A157480 A157481 A157482 * A157484 A157485 A157486
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KEYWORD
| nonn
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AUTHOR
| Vladimir Orlovsky (4vladimir(AT)gmail.com), Mar 01 2009
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EXTENSIONS
| More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu), Mar 03 2009
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