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%I #8 Apr 20 2023 07:20:16
%S 1,3,15,21,45,105,171,231,351,465,561,741,861,1275,1431,1485,2211,
%T 2415,2775,3081,3321,4005,4371,5151,7875,8385,10731,11175,11781,13041,
%U 13695,14535,15051,15225,17205,17391,17955,18915,21321,22155,23871,24531
%N Triangular numbers T such that T+2 is a prime.
%H Harvey P. Dale, <a href="/A171570/b171570.txt">Table of n, a(n) for n = 1..1000</a>
%e 1+2=3, 3+2=5, 15+2=17, ..
%t Select[s=0;Table[n*(n+1)/2,{n,6!}],PrimeQ[ #+2]&]
%t Select[Accumulate[Range[300]],PrimeQ[#+2]&] (* _Harvey P. Dale_, Jun 27 2017 *)
%Y Cf. A000217, A129545, A129752, A171569.
%K nonn
%O 1,2
%A _Vladimir Joseph Stephan Orlovsky_, Dec 11 2009
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