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Search: id:A158458
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| A158458 |
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Composite numbers k such that k+number of prime factors of k = prime. |
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+0
1
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| 8, 9, 15, 20, 21, 28, 32, 35, 39, 44, 48, 50, 51, 57, 65, 68, 69, 70, 76, 77, 87, 95, 98, 108, 110, 111, 124, 129, 135, 148, 154, 155, 161, 162, 164, 168, 170, 176, 177, 188, 189, 190, 192, 209, 221, 225, 230, 236, 237, 238, 249, 252, 264, 266, 267, 268, 272, 290
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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If composite=8=2*2*2 and 8+3=11=prime, then 8=a(1). If composite=9=3*3 and 9+2=11=prime, then 9=a(2). If composite=15=3*5 and 15+2=17=prime, then 15=a(3), etc.
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MAPLE
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for k from 4 to 400 do if not isprime(k) then if isprime(k+numtheory[bigomega](k)) then printf("%d, ", k) ; fi; fi; od: [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), May 19 2009]
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CROSSREFS
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Cf. A000040, A002808.
Sequence in context: A101765 A050688 A134334 this_sequence A079669 A047393 A037371
Adjacent sequences: A158455 A158456 A158457 this_sequence A158459 A158460 A158461
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KEYWORD
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nonn
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AUTHOR
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Juri-Stepan Gerasimov (2stepan(AT)ramblet.ru), Mar 19 2009
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EXTENSIONS
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191 replaced by 192 and extended by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), May 19 2009
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