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A162643
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Numbers whose number of divisors is not a power of 2.
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18
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4, 9, 12, 16, 18, 20, 25, 28, 32, 36, 44, 45, 48, 49, 50, 52, 60, 63, 64, 68, 72, 75, 76, 80, 81, 84, 90, 92, 96, 98, 99, 100, 108, 112, 116, 117, 121, 124, 126, 132, 140, 144, 147, 148, 150, 153, 156, 160, 162, 164, 169, 171, 172, 175, 176, 180, 188, 192, 196, 198
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OFFSET
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1,1
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COMMENTS
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The asymptotic density of this sequence is 1 - A327839 = 0.3121728605... - Amiram Eldar, Jul 28 2020
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LINKS
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FORMULA
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MATHEMATICA
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Select[Range@ 192, ! IntegerQ@ Log2@ DivisorSigma[0, #] &] (* Michael De Vlieger, Feb 24 2017 *)
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PROG
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(Haskell)
a162643 n = a162643_list !! (n-1)
a162643_list = filter ((== 0) . a209229 . a000005) [1..]
(Python)
from itertools import count, islice
from sympy import factorint
def A162643_gen(startvalue=1): # generator of terms >= startvalue
return filter(lambda n:any(map(lambda m:((k:=m+1)&-k)^k, factorint(n).values())), count(max(startvalue, 1)))
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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