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A109422 Numbers n such that tau(n)/bigomega(n) is not an integer [tau(n) =number of divisors of n; bigomega(n)=number of prime divisors of n, counted with multiplicities]. 1
4, 8, 9, 16, 25, 27, 30, 32, 36, 42, 49, 64, 66, 70, 72, 78, 81, 100, 102, 105, 108, 110, 114, 120, 121, 125, 128, 130, 138, 144, 154, 165, 168, 169, 170, 174, 180, 182, 186, 190, 195, 196, 200, 216, 222, 225, 230, 231, 238, 240, 243, 246, 252, 255, 256, 258 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Integers greater than 1 and not in A109421.

LINKS

Table of n, a(n) for n=1..56.

EXAMPLE

16 is 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.

12 is not 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

MAPLE

with(numtheory): b:=proc(n) if type(tau(n)/bigomega(n), integer)=false then n else fi end: seq(b(n), n=2..300);

MATHEMATICA

PrimeOmega[n_] := Plus @@ FactorInteger[n][[All, 2]]; Select[Range[2, 300], ! IntegerQ[DivisorSigma[0, #]/PrimeOmega[#]] &] (* Jean-Fran├žois Alcover, May 02 2013 *)

CROSSREFS

Complement of A109421.

Sequence in context: A335448 A140104 A127398 * A158804 A341645 A339497

Adjacent sequences:  A109419 A109420 A109421 * A109423 A109424 A109425

KEYWORD

nonn

AUTHOR

Emeric Deutsch, Jun 28 2005

STATUS

approved

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Last modified June 18 07:25 EDT 2021. Contains 345098 sequences. (Running on oeis4.)