A206030 Numbers m with at least two divisors d with the same sigma(d).

66, 132, 170, 198, 210, 260, 264, 322, 330, 340, 345, 396, 400, 420, 456, 462, 510, 520, 528, 594, 630, 644, 651, 660, 680, 690, 726, 780, 792, 800, 820, 840, 850, 858, 912, 924, 966, 990, 1020, 1035, 1040, 1050, 1056, 1066, 1092, 1122, 1155, 1160, 1188

Offset: 1

Author

Jaroslav Krizek, Feb 03 2012

Keywords

• nonn

Comments

Complement of sequence contains numbers whose divisors d have distinct values of sigma(d).

Examples

			66 is in sequence because two divisors d (6 and 11) of 66 have the same sigma(d) = 12.
		

Links

• Andrew Howroyd, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000203, A007609, A085790.

Programs

Mathematica

Select[Range[1200], Length[DivisorSigma[1, Divisors[#]]] != Length[Union[DivisorSigma[1, Divisors[#]]]] &] (* T. D. Noe, Feb 10 2012 *)
[Range[1200],Max[Tally[DivisorSigma[1,Divisors[#]]][[;;,2]]]>1&] (* Harvey P. Dale, Sep 27 2024 *)

PARI

ok(n)={my(v=apply(sigma, divisors(n))); #Set(v) < #v} \\ Andrew Howroyd, Aug 01 2018