A139690 a(n) = A109611(n) + 2.

4, 5, 7, 9, 13, 15, 19, 21, 25, 31, 33, 39, 43, 49, 55, 61, 69, 73, 85, 91, 103, 109, 111, 115, 129, 133, 139, 141, 151, 159, 169, 181, 183, 193, 199, 201, 213, 229, 235, 241, 253, 259, 265, 271, 283, 295, 309, 313, 319, 339, 349, 355, 361, 381, 391, 403, 411

Offset: 1

Author

Reinhard Zumkeller, Apr 29 2008

Keywords

• nonn

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..1000
• Eric Weisstein's World of Mathematics, Chen Prime

Crossrefs

Intersection of A052147 and A037143; A006512 is a subsequence.

Cf. A109611.

Programs

Mathematica

Cases[Import["https://oeis.org/A109611/b109611.txt", "Table"], {, }][[All, 2]] + 2 (* Robert Price, Apr 19 2025 *)

PARI

list(lim)=my(v=List(),t); forprime(p=2,lim\2, forprime(q=2,min(p,lim\p), if(isprime(t=p*q-2), listput(v,t+2)))); t=2; forprime(p=3,lim, if(p-t==2, listput(v,p)); t=p); Set(v) \\ Charles R Greathouse IV, Jan 19 2017

Formula

A010051(a(n)) = A139689(n); A064911(a(n)) = 1 - A139689(n);

A001222(a(n)) = 2 - A139689(n).