A085745 Numbers m such that 2^m + m is a semiprime.

2, 11, 23, 34, 59, 69, 87, 95, 119, 123, 129, 171, 197, 239, 341, 425, 455, 471, 515, 519, 635, 765, 959, 1115, 1181, 1210

Offset: 1

Author

Jason Earls, Jul 21 2003

Keywords

• nonn
• more

Comments

a(27) >= 1239. If 1239 is not a term then a(27) = 1275. - Amiram Eldar, Oct 26 2024

Links

• factordb, 2^1239+1239.

Crossrefs

Cf. A006127, A052007, A089535, A089536, A089537.

Sequences A165767, A165768, A165769 are the analog for 2^n-n. - M. F. Hasler, Oct 08 2009

Programs

Mathematica

Select[Range[1300],PrimeOmega[2^#+#]==2&] (* Harvey P. Dale, Dec 18 2014 *)

Formula

a(n) = 2*k <=> A089535(n) is even <=> A089536(n) = 2 <=> A089537(n) = 4^k/2 + k, and for any prime of this form, there is a term a(n) = 2*k in this sequence. - M. F. Hasler, Oct 08 2009

Extensions

More terms from Ray Chandler, Nov 08 2003

a(15) from Donovan Johnson, Mar 06 2008

a(16)-a(26) from Sean A. Irvine, Oct 27 2009

Offset changed to 1 by Jinyuan Wang, Jul 30 2021