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A133033
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Number of proper divisors of n-th even perfect number.
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13
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3, 5, 9, 13, 25, 33, 37, 61, 121, 177, 213, 253, 1041, 1213, 2557, 4405, 4561, 6433, 8505, 8845, 19377, 19881, 22425, 39873, 43401, 46417, 88993, 172485, 221005, 264097, 432181, 1513677, 1718865, 2515573, 2796537, 5952441, 6042753, 13945185, 26933833, 41992021, 48073165, 51929901, 60804913
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OFFSET
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1,1
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COMMENTS
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Perfect numbers: A000396(n) = 2^a(n) - 2^A090748(n), assuming there are no odd perfect numbers.
Also, a(n) is equal to the number of bits in A135650(n), the n-th even perfect number written in base 2.
These are odd numbers k such that 2^((k+1)/2) - 1 is (a Mersenne) prime. - Thomas Ordowski, Apr 20 2019
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LINKS
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FORMULA
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a(n) = A061645(n) - 1, assuming there are no odd perfect numbers.
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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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