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A039725 Even abundant numbers divided by 2.
(Formerly N1690)
3
6, 9, 10, 12, 15, 18, 20, 21, 24, 27, 28, 30, 33, 35, 36, 39, 40, 42, 44, 45, 48, 50, 51, 52, 54, 56, 57, 60, 63, 66, 69, 70, 72, 75, 78, 80, 81, 84, 87, 88, 90, 93, 96, 98, 99, 100, 102, 104, 105, 108, 110, 111, 112, 114, 117, 120, 123, 126, 129, 130, 132, 135, 136 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
While the first even abundant number is 12 = 2^2*3, the first odd abundant is 945 = 3^3*5*7, the 232nd abundant number!
The asymptotic density of this sequence is in the interval (0.491096, 0.491156) (based on the known bounds on the densities of A005101 and A005231; see A302991 and A322287). - Amiram Eldar, Mar 11 2024
REFERENCES
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
LINKS
FORMULA
a(n) = A173490(n) / 2.
EXAMPLE
The first even abundant number is 12, so 12/2 = 6 is the first element in this sequence.
MATHEMATICA
Select[Range[2, 300, 2], DivisorSigma[1, #]>2*#&]/2 (* Harvey P. Dale, Mar 22 2020 *)
CROSSREFS
Sequence in context: A177201 A090466 A090428 * A262362 A125494 A177029
KEYWORD
easy,nonn
AUTHOR
N. J. A. Sloane. This was included in the 1973 "Handbook", but was then dropped from the database. Resubmitted by James A. Sellers. Entry revised by N. J. A. Sloane, Jun 12 2012
EXTENSIONS
Corrected and edited by Daniel Forgues, Nov 22 2010
STATUS
approved

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Last modified June 22 12:42 EDT 2024. Contains 373571 sequences. (Running on oeis4.)