OFFSET
1,1
COMMENTS
Integers greater than 1 and not in A109423.
Includes all squares > 1. - Robert Israel, Jan 16 2017
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
The number 12 is in the sequence because sigma(12)=28 (1+2+3+4+6+12) and bigomega(12)=3 (2,2,3) and so sigma(12)/bigomega(12) = 28/3.
The number 24 is not in the sequence because sigma(24)=60 (1+2+3+4+6+8+12+24) and bigomega(24)=4 (2,2,2,3) and so sigma(24)/bigomega(24) = 15.
MAPLE
with(numtheory): b:=proc(n) if type(sigma(n)/bigomega(n), integer)=false then n else fi end: seq(b(n), n=2..340);
MATHEMATICA
PrimeOmega[n_] := Plus @@ FactorInteger[n][[All, 2]]; Select[Range[2, 320], ! IntegerQ[DivisorSigma[1, #]/PrimeOmega[#]] &] (* Jean-François Alcover, May 02 2013 *)
Select[Range[2, 320], !IntegerQ[DivisorSigma[1, #]/PrimeOmega[#]]&] (* Harvey P. Dale, Aug 12 2020 *)
PROG
(PARI) isok(n) = denominator(sigma(n)/bigomega(n)) != 1; \\ Michel Marcus, Jan 17 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Emeric Deutsch, Jun 28 2005
STATUS
approved