A109504 - OEIS

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

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OFFSET

1,1

LINKS

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

EXAMPLE

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

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 *)

CROSSREFS

Cf. A000217, A109611.

Sequence in context: A248483 A274424 A180528 * A122042 A291862 A217065

Adjacent sequences: A109501 A109502 A109503 * A109505 A109506 A109507

KEYWORD

easy,nonn

AUTHOR

Jason Earls, Aug 29 2005

STATUS

approved