A205524 Numbers n such that gcd(n, sigma(n)) is not equal to sigma(n) mod n.

4, 8, 9, 10, 14, 15, 16, 21, 22, 25, 26, 27, 30, 32, 33, 34, 35, 36, 38, 39, 42, 44, 45, 46, 48, 49, 50, 51, 52, 54, 55, 57, 58, 60, 62, 63, 64, 65, 66, 68, 69, 70, 72, 74, 75, 76, 77, 78, 80, 81, 82, 84, 85, 86, 87, 90, 91, 92, 93, 94, 95, 96, 98, 99, 100

Offset: 1

Author

Jaroslav Krizek, Jan 28 2012

Keywords

• nonn

Comments

All terms are nonprime numbers. Complement of A205523.

Examples

			Number 25 is in sequence because sigma(25)=31, gcd(25,31) = 1, and 31 mod 25 = 6.
		

Crossrefs

Cf. A000203, A000040, A009194, A054024, A205524, A205525.

Programs

Mathematica

Select[Range[100], Mod[GCD[#, DivisorSigma[1, #]] - DivisorSigma[1, #], #] > 0 &] (* T. D. Noe, Feb 03 2012 *)

Extensions

Corrected by T. D. Noe, Feb 03 2012