A067268 Numbers k such that k and k^2+1 have the same number of distinct prime factors.

2, 4, 12, 15, 16, 18, 22, 28, 34, 35, 38, 39, 44, 45, 46, 48, 50, 51, 52, 58, 62, 65, 68, 69, 76, 80, 82, 85, 86, 88, 92, 95, 96, 100, 104, 105, 106, 108, 118, 132, 136, 138, 141, 144, 145, 152, 158, 159, 164, 166, 171, 174, 175, 178, 188, 194, 196, 201, 202, 205

Offset: 1

Author

Benoit Cloitre, Feb 21 2002

Keywords

• easy
• nonn

Examples

			2 is a term since omega(2) = omega(2^2+1) = 1.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A001221, A002522, A128428, A272044.

Programs

Magma

[k:k in [1.. 210 ]| #PrimeDivisors(k) eq #PrimeDivisors(k^2+1)]; // Marius A. Burtea, Feb 18 2020

Mathematica

Select[Range[250],PrimeNu[#]==PrimeNu[#^2+1]&] (* Harvey P. Dale, Feb 07 2019 *)

Formula

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