A109504 Chen primes p such that p + 2 is triangular.

13, 19, 53, 89, 251, 701, 1709, 1889, 2699, 5669, 12401, 13859, 18719, 38501, 49139, 60029, 104651, 114479, 146609, 158201, 188189, 226799, 258119, 371951, 385001, 497501, 597869, 665279, 954269, 1034639, 1159001, 1309769, 1660751, 1869209

Offset: 1

Author

Jason Earls, Aug 29 2005

Keywords

• easy
• nonn

Examples

			a(9) = 2699 because it is prime and 2701 = 37*73 and 73*74/2 = 2701.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000217, A109611.

Programs

Mathematica

tri[n_] := n*(n + 1)/2; Select[tri /@ Range[2000] - 2, PrimeQ[#] && PrimeOmega[# + 2] == 2 &] (* Amiram Eldar, Dec 17 2019 *)
Select[Prime[Range[150000]],(PrimeQ[#+2]|| PrimeOmega[#+2]==2)&&OddQ[Sqrt[ 1+8(#+2)]]&] (* Harvey P. Dale, Apr 12 2021 *)