A068406 Numbers n such that n and 2n+1 have the same number of prime divisors.

2, 3, 4, 5, 8, 9, 10, 11, 13, 22, 23, 28, 29, 34, 38, 41, 45, 46, 53, 55, 57, 58, 72, 76, 77, 80, 81, 83, 85, 87, 88, 89, 91, 92, 93, 94, 100, 104, 106, 108, 112, 113, 117, 118, 121, 122, 123, 124, 125, 128, 129, 131, 133, 143, 145, 147, 148, 152, 159, 160, 161, 162

Offset: 1

Author

Benoit Cloitre, Mar 09 2002

Keywords

• easy
• nonn

Links

• Ivan Neretin, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A117360.

Programs

Mathematica

Select[Range[162], PrimeNu[#] == PrimeNu[2 # + 1] &] (* Ivan Neretin, Apr 30 2016 *)

PARI

is(n)=omega(n)==omega(2*n+1) \\ Charles R Greathouse IV, Apr 30 2016

Formula

n such that omega(n)=omega(2n+1).