A283599 Numbers k that divide sigma(k^2) - 1.

1, 2, 3, 5, 6, 7, 11, 13, 17, 18, 19, 20, 23, 29, 30, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 80, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 180, 181, 191, 193, 197, 199, 211, 223, 225, 227, 229, 233, 239, 241, 251, 257, 263, 269

Offset

1,2

Comments

Union of prime numbers (A000040) and A283744.

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Example

6 is in this sequence because 6 divides sigma(6^2) - 1 = 90.

Maple

select(n -> type((numtheory:-sigma(n^2)-1)/n, integer), [$1..1000]); # Robert Israel, Jun 20 2018

Mathematica

Select[Range@ 270, Divisible[DivisorSigma[1, #^2] - 1, #] &] (* Michael De Vlieger, Mar 15 2017 *)

Prog

(Magma) [n: n in [1..200] | Denominator(((SumOfDivisors(n^2))-1)/n) eq 1];
(PARI) for(n=1, 269, if((sigma(n^2) - 1)%n==0, print1(n, ", "))) \\ Indranil Ghosh, Mar 14 2017

Crossrefs

Cf. A000040, A065764, A283744.

Sequence in context: A062101 A330597 A352336 * A096530 A299157 A325327

Adjacent sequences: A283596 A283597 A283598 * A283600 A283601 A283602

Keyword

nonn

Author

Juri-Stepan Gerasimov, Mar 14 2017

Status

approved