A171602 - OEIS

%I #4 Mar 31 2012 12:38:28

%S 3,5,7,13,19,23,31,37,67,83,89,109,127,131,199,211,251,271,307,331,

%T 379,383,389,443,449,467,487,499,509,563,661,683,719,769,797,877,929,

%U 937,971,997,1009,1123,1163,1201,1223,1231,1237,1283,1291,1297,1307,1459

%N Lesser of two consecutive primes such that half-sums are semiprimes.

%e (3+5)/2=4->2*2, (5+7)/2=6->2*3, (7+11)/2=9->3*3, (13+17)/2=15->3*5,..

%t f[n_]:=Last/@FactorInteger[n]=={1,1}||Last/@FactorInteger[n]=={2}; lst={};Do[p=Prime[n];q=Prime[n+1];s=(p+q)/2;If[f[s],AppendTo[lst,p]],{n,6!}];lst

%K nonn

%O 1,1

%A _Vladimir Joseph Stephan Orlovsky_, Dec 12 2009