A067886 Numbers k such that 2^k+1 and 2^k-1 have the same number of distinct prime factors.

2, 3, 6, 9, 11, 14, 15, 18, 21, 23, 27, 29, 33, 42, 47, 51, 53, 54, 57, 69, 71, 73, 74, 81, 82, 86, 95, 101, 105, 111, 113, 114, 115, 121, 129, 130, 138, 141, 142, 165, 167, 169, 179, 181, 199, 203, 209, 213, 230, 233, 235, 243, 250, 255, 258, 277, 279, 306, 307

Offset

1,1

Comments

Numbers k such that omega(2^k+1) = omega(2^k-1).

Links

Amiram Eldar, Table of n, a(n) for n = 1..141

Mathematica

sndpQ[n_]:=Module[{c=2^n}, PrimeNu[c+1]==PrimeNu[c-1]]; Select[Range[ 250], sndpQ] (* Harvey P. Dale, Feb 04 2016 *)

Prog

(PARI) isok(k) = omega(2^k-1) == omega(2^k+1); \\ Michel Marcus, Feb 13 2020
(Magma) [k: k in [2..307] | #PrimeDivisors(2^k-1) eq #PrimeDivisors(2^k+1) ]; // Marius A. Burtea, Feb 13 2020

Crossrefs

Cf. A001221, A046799, A046800.

Sequence in context: A118730 A291669 A097384 * A227000 A338546 A358130

Adjacent sequences: A067883 A067884 A067885 * A067887 A067888 A067889

Keyword

nonn

Author

Benoit Cloitre, Mar 02 2002

Extensions

More terms from Rick L. Shepherd, May 14 2002

More terms from Amiram Eldar, Feb 13 2020

Status

approved