Displaying similar documents to “Almost perfect domains”

On near-perfect and deficient-perfect numbers

Min Tang, Xiao-Zhi Ren, Meng Li (2013)

Colloquium Mathematicae

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For a positive integer n, let σ(n) denote the sum of the positive divisors of n. Let d be a proper divisor of n. We call n a near-perfect number if σ(n) = 2n + d, and a deficient-perfect number if σ(n) = 2n - d. We show that there is no odd near-perfect number with three distinct prime divisors and determine all deficient-perfect numbers with at most two distinct prime factors.

Odd perfect numbers of a special form

Tomohiro Yamada (2005)

Colloquium Mathematicae

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We show that there is an effectively computable upper bound of odd perfect numbers whose Euler factors are powers of fixed exponent.

Rings whose proper factors are right perfect

Alberto Facchini, Catia Parolin (2011)

Colloquium Mathematicae

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We show that practically all the properties of almost perfect rings, proved by Bazzoni and Salce [Colloq. Math. 95 (2003)] for commutative rings, also hold in the non-commutative setting.

A basic approach to the perfect extensions of spaces

Giorgio Nordo (1997)

Commentationes Mathematicae Universitatis Carolinae

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In this paper we generalize the notion of of a Tychonoff space to a generic extension of any space by introducing the concept of . This allow us to simplify the treatment in a basic way and in a more general setting. Some [S 1 ], [S 2 ], and [D]’s results are improved and new characterizations for perfect (Hausdorff) extensions of spaces are obtained.