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A321213
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a(n) is the number of divisors of n-th Fermat number (A000215).
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0
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2, 2, 2, 2, 2, 4, 4, 4, 4, 8, 16, 32
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OFFSET
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0,1
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LINKS
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FORMULA
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EXAMPLE
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A000215(n) is prime for n=0 to 4, so a(n)= 2 for n=0 to 4.
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MATHEMATICA
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Table[DivisorSigma[0, 2^2^n + 1], {n, 120}]
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PROG
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(PARI) a(n) = numdiv(2^2^n+1)
(Magma) [DivisorSigma(0, 2^2^n + 1): n in [1..100]]
(GAP) List(List([0..11], n->2^(2^n)+1), i->Number(DivisorsInt(i))); # Muniru A Asiru, Nov 03 2018
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CROSSREFS
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KEYWORD
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nonn,more,hard
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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