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

1,1

Comments

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

Links

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

Example

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

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 *)

Prog

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

Crossrefs

Cf. A000203, A007609, A085790.

Sequence in context: A118163 A160848 A160278 * A174929 A072430 A278126

Adjacent sequences: A206027 A206028 A206029 * A206031 A206032 A206033

Keyword

nonn

Author

Jaroslav Krizek, Feb 03 2012

Status

approved