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Search: id:A030513
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| A030513 |
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Numbers with 4 divisors. |
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+0
20
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| 6, 8, 10, 14, 15, 21, 22, 26, 27, 33, 34, 35, 38, 39, 46, 51, 55, 57, 58, 62, 65, 69, 74, 77, 82, 85, 86, 87, 91, 93, 94, 95, 106, 111, 115, 118, 119, 122, 123, 125, 129, 133, 134, 141, 142, 143, 145, 146, 155, 158, 159, 161, 166, 177, 178, 183, 185, 187
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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4*a(n) are the solutions to A048272(x)=sum(d/x,(-1)^d)=4 - Benoit Cloitre (benoit7848c(AT)orange.fr), Apr 14 2002
Numbers which are the geometric counterpart of perfect numbers (equal to the sum of their proper divisors), i.e. equal to the product of their proper divisors. - Lekraj Beedassy (blekraj(AT)yahoo.com), Jul 10 2003
Or, numbers with 3 perfect partitions. - Juri-Stepan Gerasimov (2stepan(AT)rambler.ru), Oct 10 2009
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LINKS
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R. J. Mathar, Table of n, a(n) for n = 1..455
Anonymous, Multiplicatively Perfect Numbers
R. J. Mathar, Maple programs for A030638, A030637, A030636, A030635, A030634, A030633, A030632, A030631, A030630, A030629, A030628, A030627, A030626, A030516, A030515, A030514, A030513
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FORMULA
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Numbers which are either the product of two distinct primes (A006881) or the cube of a prime (A030078)
A000005(a(n))=4 or A002033(a(n))=3. - Juri-Stepan Gerasimov (2stepan(AT)rambler.ru), Oct 10 2009
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CROSSREFS
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Cf. A007422, A030515, etc., A035533.
Cf. A000005, A002033. - Juri-Stepan Gerasimov (2stepan(AT)rambler.ru), Oct 10 2009
Sequence in context: A036436 A036455 A007422 this_sequence A161918 A152126 A065858
Adjacent sequences: A030510 A030511 A030512 this_sequence A030514 A030515 A030516
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KEYWORD
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nonn,easy,nice
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AUTHOR
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Jeff Burch (jmburch(AT)osprey.smcm.edu)
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EXTENSIONS
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Edited by Juri-Stepan Gerasimov (2stepan(AT)rambler.ru), Oct 10 2009
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