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A037291
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Number of rings with 1 containing n elements.
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18
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1, 1, 1, 4, 1, 1, 1, 11, 4, 1, 1, 4, 1, 1, 1, 50, 1, 4, 1, 4, 1, 1, 1, 11, 4, 1, 12, 4, 1, 1, 1, 208, 1, 1, 1, 16, 1, 1, 1, 11, 1, 1, 1, 4, 4, 1, 1, 50, 4, 4, 1, 4, 1, 12, 1, 11, 1, 1, 1, 4, 1, 1, 4
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OFFSET
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1,4
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COMMENTS
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Many authors simply call these "rings". They are also known as unital rings, rings with unity, or rings with identity. - Charles R Greathouse IV, Aug 12 2015
Is this sequence multiplicative? That is, if p and q are distinct primes, is it true that a(p^i*q^j) = a(p^i)*a(q^j)? - Jianing Song, Oct 26 2019. The answer is yes - see the Eric M. Rains link. - N. J. A. Sloane, Oct 27 2019
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LINKS
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CROSSREFS
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KEYWORD
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nonn,nice,hard,mult
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AUTHOR
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EXTENSIONS
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a(16) and a(32)-a(63) from Christof Noebauer (christof.noebauer(AT)algebra.uni-linz.ac.at), Sep 29 2000
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STATUS
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approved
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