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A046798
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Number of divisors of 2^n + 1.
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20
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2, 2, 2, 3, 2, 4, 4, 4, 2, 8, 6, 4, 4, 4, 8, 12, 2, 4, 16, 4, 4, 12, 8, 4, 8, 16, 16, 20, 4, 8, 48, 4, 4, 24, 16, 32, 16, 8, 16, 12, 4, 8, 64, 4, 8, 64, 32, 8, 8, 8, 64, 48, 8, 8, 64, 48, 8, 24, 8, 16, 16, 4, 32, 64, 4, 64, 64, 8, 12, 24, 96, 8, 32, 8, 32, 96, 16, 64, 768, 4, 8, 192, 32, 64
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OFFSET
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0,1
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COMMENTS
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a(n) is odd iff n = 3, as a consequence of the Catalan-Mihăilescu theorem. - Bernard Schott, Oct 05 2021
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LINKS
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FORMULA
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EXAMPLE
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a(7)=4, because 2^7 + 1 = 129 has 4 divisors.
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MAPLE
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a:= n-> numtheory[tau](2^n+1):
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MATHEMATICA
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DivisorSigma[0, 1 + 2^#] & /@ Range[0, 83] (* Jayanta Basu, Jun 29 2013 *)
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PROG
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(Python)
from sympy.ntheory import divisor_count
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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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