OFFSET
1,1
COMMENTS
Integers greater than 1 and not in A109422.
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
EXAMPLE
12 is in the sequence because tau(12)=6 (1,2,3,4,6,12) and bigomega(12)=3 (2,2,3) and so tau(12)/bigomega(12)=2.
16 is not in the sequence because tau(16)=5 (1,2,4,8,16) and bigomega(16)=4 (2,2,2,2) and so tau(16)/bigomega(16)=5/4.
MAPLE
with(numtheory): a:=proc(n) if type(tau(n)/bigomega(n), integer)=true then n else fi end: seq(a(n), n=2..110);
MATHEMATICA
f[n_] := DivisorSigma[0, n]/Plus @@ Last /@ FactorInteger[n]; Select[ Range[2, 89], IntegerQ[ f[ # ]] &] (* Robert G. Wilson v, Jun 29 2005 *)
Select[Range[2, 100], IntegerQ[DivisorSigma[0, #]/PrimeOmega[#]]&] (* Harvey P. Dale, Aug 14 2019 *)
PROG
(PARI) is(n)=my(f=factor(n)); n>1 && numdiv(f)%vecsum(f[, 2])==0 \\ Charles R Greathouse IV, Apr 27 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Emeric Deutsch, Jun 28 2005
STATUS
approved