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Numbers which are not divisible by the number of their prime factors (counted with multiplicity).
13

%I #18 May 13 2023 13:12:05

%S 8,9,15,20,21,25,28,32,33,35,39,44,48,49,50,51,52,54,55,57,64,65,68,

%T 69,70,72,76,77,81,85,87,90,91,92,93,95,98,108,110,111,112,115,116,

%U 119,121,123,124,125,126,128,129,130,133,135,141,143,145,148,150,154,155,159

%N Numbers which are not divisible by the number of their prime factors (counted with multiplicity).

%C The asymptotic density of this sequence is 1 (Erdős and Pomerance, 1990). - _Amiram Eldar_, Jul 10 2020

%H Hieronymus Fischer, <a href="/A134334/b134334.txt">Table of n, a(n) for n = 1..10000</a>

%H Paul Erdős and Carl Pomerance, <a href="https://math.dartmouth.edu/~carlp/PDF/paper79.pdf">On a theorem of Besicovitch: values of arithmetic functions that divide their arguments</a>, Indian J. Math., Vol. 32 (1990), pp. 279-287.

%e a(1) = 8, since 8 = 2*2*2 has 3 prime factors and 8 is not divisible by 3.

%e a(3) = 15, since 15 = 3*5 has 2 prime factors and 15 is not divisible by 2.

%t Select[Range[2,200],Mod[#,PrimeOmega[#]]!=0&] (* _Harvey P. Dale_, May 13 2023 *)

%o (PARI) isok(n) = (n % bigomega(n)) \\ _Michel Marcus_, Jul 15 2013

%Y Cf. A000040, A001222, A074946 (complement), A100118, A046363, A133620, A133621.

%Y Cf. A133880, A133890, A133900, A133910, A133911, A046346, A134331, A134332, A134333, A134335, A134344, A134376.

%K nonn

%O 1,1

%A _Hieronymus Fischer_, Oct 23 2007