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A152921
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a(n) = 2^(2p-1)/2, where p is A000043(n).
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4
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4, 16, 256, 4096, 16777216, 4294967296, 68719476736, 1152921504606846976, 1329227995784915872903807060280344576, 95780971304118053647396689196894323976171195136475136, 6582018229284824168619876730229402019930943462534319453394436096
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OFFSET
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1,1
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COMMENTS
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Ultraperfect numbers (A139306), divided by 2.
Also, a(n) is the largest proper divisor of the n-th ultraperfect number.
These cototients are squares = (2^(p-1))^2. - Bernard Schott, Mar 14 2022
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LINKS
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FORMULA
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MATHEMATICA
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a[n_] := 4^(MersennePrimeExponent[n] - 1); Array[a, 12] (* Amiram Eldar, Mar 06 2022 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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