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 A164620 Primes p such that 1 +p*floor(p/2) is also prime. 4
 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; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 EXAMPLE p=2 qualifies since 2*1+1=3 is prime. p=5 qualifies since 5*2+1=11 is prime. MATHEMATICA lst={}; Do[p=Prime[n]; If[PrimeQ[p*Floor[p/2]+1], AppendTo[lst, p]], {n, 3*6!}]; lst Select[Prime[Range[350]], PrimeQ[1+#*Floor[#/2]]&] (* Harvey P. Dale, Apr 07 2015 *) CROSSREFS Cf. A008846, A020882, A158708. Sequence in context: A102854 A156009 A215275 * A333876 A156013 A112634 Adjacent sequences: A164617 A164618 A164619 * A164621 A164622 A164623 KEYWORD nonn,easy AUTHOR Vladimir Joseph Stephan Orlovsky, Aug 17 2009 EXTENSIONS Comments turned into examples by R. J. Mathar, Sep 17 2009 STATUS approved

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Last modified May 29 00:29 EDT 2024. Contains 372921 sequences. (Running on oeis4.)