A125493 - OEIS

%I #12 Jan 06 2019 04:05:27

%S 4,8,9,10,14,15,16,21,22,25,26,27,32,33,34,35,38,39,44,45,46,49,50,51,

%T 52,55,57,58,62,63,64,65,68,69,74,75,76,77,81,82,85,86,87,91,92,93,94,

%U 95,98,99,105,106,110,111,115,116,117,118,119,121,122,123,124,125,128

%N Composite deficient numbers.

%H Harvey P. Dale, <a href="/A125493/b125493.txt">Table of n, a(n) for n = 1..1000</a>

%e 22 is in the sequence because it is composite and its sum of divisors 1 + 2 + 11 + 22 = 36 is less than 2*22.

%e 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.

%p 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

%t Select[Range[200],CompositeQ[#]&&DivisorSigma[1,#]<2#&] (* _Harvey P. Dale_, Mar 27 2016 *)

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

%K nonn

%O 1,1

%A _Tanya Khovanova_, Dec 27 2006

%E More terms from _Emeric Deutsch_, Jan 01 2007