OFFSET
1,1
COMMENTS
A subsequence of A023198 (numbers with abundancy >= 4). It differs from A023198 from a(31093) on: The term A023198(31093) = 122522400 = A023199(5) = A215264(1) is not in this sequence. It excludes all terms of A215264, but also the 5-perfect numbers A046060, which are neither in this sequence nor in A215264. [Corrected by M. F. Hasler, Dec 05 2013]
A108775(a(n)) = 4.
There are 31092 terms less than 122522399. - T. D. Noe, Dec 04 2013
LINKS
Jaroslav Krizek, Table of n, a(n) for n = 1..1000
Eric Weisstein's World of Mathematics, Abundancy
Eric Weisstein's World of Mathematics, Abundant Number
EXAMPLE
27720 is in sequence because sigma(27720) / 27720 = 112320 / 27720 = 4.0519....
MATHEMATICA
Select[Range[200000], 4 <= DivisorSigma[1, #]/# < 5 &] (* T. D. Noe, Dec 04 2013 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, Nov 29 2013
EXTENSIONS
Corrected and edited by M. F. Hasler, Dec 05 2013
STATUS
approved