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%I #5 Mar 30 2012 18:38:46
%S 4,13,15,19,21,27,31,35,37,39,51,53,57,65,67,69,77,83,87,89,95,109,
%T 111,113,125,127,129,131,139,155,157,161,177,181,199,209,211,221,233,
%U 237,249,251,257,263,267,291,293,305,307,309,317,329,335,337,353,365,371
%N A066728(a(n))=3.
%C Conjecture: the set of k such that a(k+1)-a(k)=2 is infinite.
%F If a(k+1)-a(k)=2 then a(k) or a(k+1) is prime. For example : a(9)-a(8)=37-35 and a(9)=37 is prime. a(16)-a(15)=69-67=2 and a(15)=67 is prime.
%Y Cf. A066728.
%K nonn
%O 1,1
%A _Benoit Cloitre_, Jan 16 2002
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