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Search: id:A164385
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| A164385 |
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Composite numbers c such that c+4 and c-4 are both prime. |
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+0
1
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| 9, 15, 27, 33, 57, 63, 75, 93, 105, 135, 153, 177, 195, 237, 267, 273, 363, 393, 405, 435, 453, 483, 495, 567, 573, 597, 603, 657, 687, 705, 723, 747, 765, 825, 915, 933, 987, 1017, 1035, 1065, 1113, 1167, 1197, 1227, 1233, 1287, 1293, 1323, 1377, 1443, 1455, 1485
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Composite numbers of the form A023202(k)+4, any k.
A087680 without the {7} [Proof: there are no 3 primes in arithmetic progression p, p+4, p+8, except p=3.
If p=3*l+1, p+8 were divisible by 3, and if p=3*l+2, p+4 were divisible by 3. R. J. Mathar, Aug 20 2009]
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FORMULA
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A164383 INTERSECT A164384.
A087680 INTERSECT A002808.
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EXAMPLE
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a(1)=5(prime)+4=13(prime)-4=9(composite). a(2)=11(prime)+4=19(prime)-4=15(composite).
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CROSSREFS
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Cf. A000040, A002808.
Sequence in context: A082549 A013569 A129401 this_sequence A046353 A046356 A060874
Adjacent sequences: A164382 A164383 A164384 this_sequence A164386 A164387 A164388
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KEYWORD
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nonn
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AUTHOR
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Juri-Stepan Gerasimov (2stepan(AT)rambler.ru), Aug 14 2009
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EXTENSIONS
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65 removed, 337 changed to 237 etc. by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Aug 20 2009
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