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Non-Fibonacci numbers with non-Fibonacci number of divisors.
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%I #10 Jun 20 2021 17:06:52

%S 6,10,12,14,15,18,20,22,26,27,28,32,33,35,36,38,39,44,45,46,48,50,51,

%T 52,57,58,60,62,63,64,65,68,69,72,74,75,76,77,80,82,84,85,86,87,90,91,

%U 92,93,94,95,96,98,99,100,106,108,111

%N Non-Fibonacci numbers with non-Fibonacci number of divisors.

%C A000005(a(n)) is not a Fibonacci number.

%H Harvey P. Dale, <a href="/A139587/b139587.txt">Table of n, a(n) for n = 1..1000</a>

%e 6 belongs to the sequence because it is not a Fibonacci number and its number of divisors, 4, is also not a Fibonacci number.

%t With[{fibs=Fibonacci[Range[12]]},Select[Range[Max[fibs]],FreeQ[fibs,#] && FreeQ[fibs,DivisorSigma[0,#]]&]] (* _Harvey P. Dale_, Jun 20 2021 *)

%Y Non-Fibonacci number: A001690. Cf. A000005, A000045, A139095, A139586, A139588, A139589, A139590.

%K easy,nonn

%O 1,1

%A _Omar E. Pol_, May 22 2008

%E Example clarified by _Harvey P. Dale_, Jun 20 2021