A246454 Numbers k that divide 2*sigma(k).

1, 2, 6, 24, 28, 120, 496, 672, 4320, 4680, 8128, 26208, 30240, 32760, 523776, 2178540, 8910720, 17428320, 20427264, 23569920, 33550336, 45532800, 91963648, 142990848, 197064960, 459818240, 1379454720, 1476304896, 8583644160, 8589869056, 10200236032

Offset

1,2

Comments

Numbers k such that 2*(A000203(k)) / k) is an integer.

Union of A007691 (multiply-perfect numbers) and A159907 (numbers with half-integral abundancy index).

Links

Jens Kruse Andersen, Table of n, a(n) for n = 1..55

Example

Number 24 is in the sequence because 24 divides 2*sigma(24); 24 divides 2*60.

Prog

(Magma) [n: n in [1..1000000] | Denominator(2*(SumOfDivisors(n))/n) eq 1]
(PARI)
for(n=1, 10^8, if((2*sigma(n))%n==0, print1(n, ", "))) \\ Derek Orr, Aug 26 2014

Crossrefs

Cf. A000203, A007691, A159907.

Sequence in context: A123145 A232981 A304039 * A079433 A319205 A110728

Adjacent sequences: A246451 A246452 A246453 * A246455 A246456 A246457

Keyword

nonn

Author

Jaroslav Krizek, Aug 26 2014

Status

approved