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%I #12 Apr 12 2021 15:00:54
%S 13,19,53,89,251,701,1709,1889,2699,5669,12401,13859,18719,38501,
%T 49139,60029,104651,114479,146609,158201,188189,226799,258119,371951,
%U 385001,497501,597869,665279,954269,1034639,1159001,1309769,1660751,1869209
%N Chen primes p such that p + 2 is triangular.
%H Amiram Eldar, <a href="/A109504/b109504.txt">Table of n, a(n) for n = 1..10000</a>
%e a(9) = 2699 because it is prime and 2701 = 37*73 and 73*74/2 = 2701.
%t tri[n_] := n*(n + 1)/2; Select[tri /@ Range[2000] - 2, PrimeQ[#] && PrimeOmega[# + 2] == 2 &] (* _Amiram Eldar_, Dec 17 2019 *)
%t Select[Prime[Range[150000]],(PrimeQ[#+2]|| PrimeOmega[#+2]==2)&&OddQ[Sqrt[ 1+8(#+2)]]&] (* _Harvey P. Dale_, Apr 12 2021 *)
%Y Cf. A000217, A109611.
%K easy,nonn
%O 1,1
%A _Jason Earls_, Aug 29 2005
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