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%I #4 Jul 23 2012 17:06:31
%S 2,3,7,11,13,17,31,67,157,229,379,487,1291,1621,3217,3727,4051,4621,
%T 6007,7129,7879,9157,9661,10531,11071,12577,13567,15877,16987,23629,
%U 24979,28081,31981,32917,39847,46687,51679,54877,56101,58171,61561
%N Primes of the form p=floor(T/6), T are triangular numbers.
%H Harvey P. Dale, <a href="/A171595/b171595.txt">Table of n, a(n) for n = 1..1000</a>
%e Floor(15/6)=2, floor(21/6)=3, floor(45/6)=7,..
%t f[n_]:=n*(n+1)/2;lst={};Do[If[PrimeQ[p=Floor[f[n]/6]],AppendTo[lst,p]],{n,7!}];lst
%t Select[Floor[#/6]&/@Accumulate[Range[1000]],PrimeQ] (* _Harvey P. Dale_, Jul 23 2012 *)
%Y Cf. A000217, A171574
%K nonn
%O 1,1
%A _Vladimir Joseph Stephan Orlovsky_, Dec 12 2009