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The probability that a complete intersection is smooth

Alina Bucur, Kiran S. Kedlaya (2012)

Journal de Théorie des Nombres de Bordeaux

Given a smooth subscheme of a projective space over a finite field, we compute the probability that its intersection with a fixed number of hypersurface sections of large degree is smooth of the expected dimension. This generalizes the case of a single hypersurface, due to Poonen. We use this result to give a probabilistic model for the number of rational points of such a complete intersection. A somewhat surprising corollary is that the number of rational points on a random smooth intersection...

The R₂ measure for totally positive algebraic integers

V. Flammang (2016)

Colloquium Mathematicae

Let α be a totally positive algebraic integer of degree d, i.e., all of its conjugates α = α , . . . , α d are positive real numbers. We study the set ₂ of the quantities ( i = 1 d ( 1 + α ² i ) 1 / 2 ) 1 / d . We first show that √2 is the smallest point of ₂. Then, we prove that there exists a number l such that ₂ is dense in (l,∞). Finally, using the method of auxiliary functions, we find the six smallest points of ₂ in (√2,l). The polynomials involved in the auxiliary function are found by a recursive algorithm.

The range of the sum-of-proper-divisors function

Florian Luca, Carl Pomerance (2015)

Acta Arithmetica

Answering a question of Erdős, we show that a positive proportion of even numbers are in the form s(n), where s(n) = σ(n) - n, the sum of proper divisors of n.

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