A125493 Composite deficient numbers.

4, 8, 9, 10, 14, 15, 16, 21, 22, 25, 26, 27, 32, 33, 34, 35, 38, 39, 44, 45, 46, 49, 50, 51, 52, 55, 57, 58, 62, 63, 64, 65, 68, 69, 74, 75, 76, 77, 81, 82, 85, 86, 87, 91, 92, 93, 94, 95, 98, 99, 105, 106, 110, 111, 115, 116, 117, 118, 119, 121, 122, 123, 124, 125, 128

Offset

1,1

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Example

22 is in the sequence because it is composite and its sum of divisors 1 + 2 + 11 + 22 = 36 is less than 2*22.
The integer 15 is in the sequence because it is composite and the sum of its proper divisors is 1 + 3 + 5 < 15. The integer 18 is not in the sequence because, although composite, the sum of its proper divisors is 1 + 2 + 3 + 6 + 9 > 18.

Maple

with(numtheory): a:=proc(n) if sigma(n)<2*n and bigomega(n)>1 then n else fi end: seq(a(n), n=1..160); # Emeric Deutsch, Jan 01 2007

Mathematica

Select[Range[200], CompositeQ[#]&&DivisorSigma[1, #]<2#&] (* Harvey P. Dale, Mar 27 2016 *)

Crossrefs

Cf. A002808 (composite numbers), A005100 (deficient numbers).

Sequence in context: A274584 A210998 A205524 * A341615 A164923 A141608

Adjacent sequences: A125490 A125491 A125492 * A125494 A125495 A125496

Keyword

nonn

Author

Tanya Khovanova, Dec 27 2006

Extensions

More terms from Emeric Deutsch, Jan 01 2007

Status

approved