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Search: id:A164620
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| A164620 |
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Primes p such that 1 +p*floor(p/2) is also prime. |
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+0
4
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| 2, 5, 13, 17, 41, 61, 89, 97, 101, 113, 149, 173, 229, 241, 281, 317, 349, 353, 373, 397, 409, 421, 433, 461, 509, 521, 661, 673, 761, 853, 881, 937, 941, 1013, 1093, 1109, 1249, 1289, 1297, 1373, 1433, 1549, 1741, 1753, 1913, 2113, 2213, 2269, 2281, 2297
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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p=2 qualifies since 2*1+1=3 is prime. p=5 qualifies since 5*2+1=11 is prime.
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MATHEMATICA
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lst={}; Do[p=Prime[n]; If[PrimeQ[p*Floor[p/2]+1], AppendTo[lst, p]], {n, 3*6!}]; lst
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CROSSREFS
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Cf. A008846, A020882, A158708
Sequence in context: A079936 A102854 A156009 this_sequence A156013 A112634 A045364
Adjacent sequences: A164617 A164618 A164619 this_sequence A164621 A164622 A164623
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KEYWORD
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nonn
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AUTHOR
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Vladimir Orlovsky (4vladimir(AT)gmail.com), Aug 17 2009
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EXTENSIONS
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Comments turned into examples by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Sep 17 2009
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