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A342375
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Number of commutative rings without 1 containing n elements.
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3
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0, 1, 1, 5, 1, 3, 1, 24, 5, 3, 1, 14, 1, 3, 3, 125, 1, 14, 1, 14, 3, 3, 1, 58, 5, 3, 25, 14, 1, 7, 1
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OFFSET
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1,4
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COMMENTS
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A ring without 1 is still a ring, but sometimes it is called a rng, or a non-unital ring, or a pseudo-ring (see Wikipedia links).
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LINKS
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FORMULA
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EXAMPLE
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a(1) = 0 because the only ring with 1 element is the zero ring with the element 0, and for this ring, 0 and 1 coincide.
a(2) = 1, and for this corresponding ring with elements {0,a}, the multiplication that is defined by: 0*0 = 0*a = a*0 = a*a = 0 is commutative, also this ring is without unit, hence a(2) = 1; the Matrix ring {0,a} with coefficients from Z/2Z:
(0 0) (0 0)
0 = (0 0) a = (1 0) is such an example.
For n=8, there are 52 rings of order 8, 24 of which are commutative rings without 1, so a(8) = 24.
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CROSSREFS
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Number of commutative rings: A127707 (with 1 containing n elements), this sequence (without 1 containing n elements), A037289 (with n elements).
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KEYWORD
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nonn,more
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AUTHOR
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STATUS
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approved
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