A067886 - OEIS

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

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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