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

1,1

Comments

All terms are nonprime numbers. Complement of A205523.

Links

Table of n, a(n) for n=1..65.

Example

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

Mathematica

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

Crossrefs

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

Sequence in context: A288862 A274584 A210998 * A125493 A341615 A164923

Adjacent sequences: A205521 A205522 A205523 * A205525 A205526 A205527

Keyword

nonn

Author

Jaroslav Krizek, Jan 28 2012

Extensions

Corrected by T. D. Noe, Feb 03 2012

Status

approved