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%I #9 Mar 08 2015 21:30:49
%S 3,5,11,14,18,20,26,27,28,29,31,38,42,52,58,64,73,82,85,90,110,125,
%T 138,156,167,180,212,234,248,297,299,303,305,308,312,314,317,319,334,
%U 336,348,361,365,371,372,377,379,414,451,465,478,499,508,509,535,554,564
%N Numbers n such that 252n^2 is the average of a twin prime pair.
%C Inspired by _Zak Seidov_'s post to the SeqFan list, cf. link: This yields A154673 as 252 a(n)^2. Indeed, if N/7 is a square, then N=7m^2 and this can't be the average of a twin prime pair unless m=6a.
%H Zak Seidov, <a href="http://zak08.livejournal.com/4070.html">"A154676"</a>, Jan 15 2009
%F a(n) = sqrt(A154673(n)/252).
%t Select[Range[600],And@@PrimeQ[252#^2+{1,-1}]&] (* _Harvey P. Dale_, Dec 13 2012 *)
%o (PARI) for(i=1,999, isprime(252*i^2+1) & isprime(252*i^2-1) & print1(i","))
%Y Cf. A037073, A154331, A154772.
%K nonn
%O 1,1
%A _M. F. Hasler_, Jan 15 2009
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