|
|
A109510
|
|
Values of n such that sigma(n)-2n (the abundance of n) is a (nonnegative) square.
|
|
3
|
|
|
6, 12, 28, 70, 88, 108, 168, 220, 348, 496, 550, 580, 726, 748, 798, 910, 918, 952, 1032, 1120, 1200, 1240, 1504, 1644, 1672, 1840, 1888, 2140, 2205, 2392, 2470, 2472, 2814, 3190, 3222, 3580, 3804, 4030, 4648, 4732, 4758, 5032, 5670, 5830
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
LINKS
|
Eric Weisstein's World of Mathematics, Abundance
|
|
EXAMPLE
|
12 is in the sequence since sigma(12) - 2*12 = 28 - 24 = 4 = 2^2 is a square.
|
|
MATHEMATICA
|
Select[Range[6000], IntegerQ@Sqrt[DivisorSigma[1, #] - 2 #] &] (* Amiram Eldar, Jun 22 2019 *)
|
|
PROG
|
(PARI) isok(n) = issquare(sigma(n) - 2*n); \\ Michel Marcus, Jun 22 2019
|
|
CROSSREFS
|
Cf. A000396 (perfect numbers: a subsequence).
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|