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%I #8 Apr 07 2015 10:50:45
%S 2,5,13,17,41,61,89,97,101,113,149,173,229,241,281,317,349,353,373,
%T 397,409,421,433,461,509,521,661,673,761,853,881,937,941,1013,1093,
%U 1109,1249,1289,1297,1373,1433,1549,1741,1753,1913,2113,2213,2269,2281,2297
%N Primes p such that 1 +p*floor(p/2) is also prime.
%H Vincenzo Librandi, <a href="/A164620/b164620.txt">Table of n, a(n) for n = 1..1000</a>
%e p=2 qualifies since 2*1+1=3 is prime. p=5 qualifies since 5*2+1=11 is prime.
%t lst={};Do[p=Prime[n];If[PrimeQ[p*Floor[p/2]+1],AppendTo[lst,p]],{n,3*6!}]; lst
%t Select[Prime[Range[350]],PrimeQ[1+#*Floor[#/2]]&] (* _Harvey P. Dale_, Apr 07 2015 *)
%Y Cf. A008846, A020882, A158708.
%K nonn,easy
%O 1,1
%A _Vladimir Joseph Stephan Orlovsky_, Aug 17 2009
%E Comments turned into examples by _R. J. Mathar_, Sep 17 2009