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A037289
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Number of commutative rings with n elements.
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15
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1, 2, 2, 9, 2, 4, 2, 34, 9, 4, 2, 18, 2, 4, 4, 162, 2, 18, 2, 18, 4, 4, 2, 68, 9, 4, 36, 18, 2, 8, 2
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OFFSET
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1,2
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COMMENTS
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These rings do not necessarily contain an identity element.
This sequence is multiplicative. See the reference "The Numbers of Small Rings" below, which proves the result for all rings; restricting to commutative rings only makes the proof easier. - Conjecture by Mitch Harris, Apr 19 2005, proof found by Franklin T. Adams-Watters, Jul 10 2012
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LINKS
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C. Noebauer, Home page [Archived copy as of 2008 from web.archive.org]
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FORMULA
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CROSSREFS
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KEYWORD
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nonn,nice,more,hard,mult
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AUTHOR
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EXTENSIONS
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a(16) from Christof Noebauer (christof.noebauer(AT)algebra.uni-linz.ac.at), Sep 29 2000, who reports that the sequence continues a(32) = ? (> 876), a(33) = 4, 4, 4, 81, 2, 4, 4, 68, 2, 8, 2, 18, 18, 4, 2, 324, 9, 18, 4, 18, 2, 72, 4, 68, 4, 4, 2, 36, 2, 4, 18 = a(63), a(64) = ? (> 12696)
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STATUS
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approved
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