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 A133033 Number of proper divisors of n-th even perfect number. 13
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 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. LINKS Ivan Panchenko, Table of n, a(n) for n = 1..47 C. K. Caldwell, "Top Twenty" page, Mersenne Primes. FORMULA a(n) = A061645(n) - 1, assuming there are no odd perfect numbers. a(n) = A000043(n) + A090748(n) = 2*A000043(n) - 1 = 2*A090748(n) + 1. CROSSREFS Cf. A135650. Sequence in context: A153263 A295140 A144933 * A145365 A146433 A134672 Adjacent sequences:  A133030 A133031 A133032 * A133034 A133035 A133036 KEYWORD nonn AUTHOR Omar E. Pol, Oct 27 2007, Feb 23 2008, Apr 28 2009 EXTENSIONS a(39)-a(43) from Ivan Panchenko, Apr 12 2018 STATUS approved

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Last modified May 27 13:51 EDT 2018. Contains 304694 sequences. (Running on oeis4.)