%I #11 May 31 2013 03:41:37
%S 15,19,21,23,25,31,37,39,57,67,75,77,83,99,107,111,115,145,165,175,
%T 189,195,207,235,237,247,273,293,303,311,315,337,351,353,361,395,405,
%U 439,445,471,477,493,495,499,537,545,555,567,569,581,585,591,619,631
%N Numbers n such that (n + prime(n))/2 is a prime.
%C Average of n and n-th prime is a prime. All n must be odd.
%H Paolo P. Lava, <a href="/A225861/b225861.txt">Table of n, a(n) for n = 1..1000</a>
%e 15 is in the list since (15+Prime(15))/2=31.
%t Select[Range[632], PrimeQ[(# + Prime[#])/2] &]
%Y Cf. A000040.
%K nonn
%O 1,1
%A _Jayanta Basu_, May 18 2013
|