A067268 - OEIS

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

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

LINKS

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

FORMULA

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

EXAMPLE

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

MATHEMATICA

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

PROG