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Goldbach’s problem with primes in arithmetic progressions and in short intervals

Karin Halupczok (2013)

Journal de Théorie des Nombres de Bordeaux

Some mean value theorems in the style of Bombieri-Vinogradov’s theorem are discussed. They concern binary and ternary additive problems with primes in arithmetic progressions and short intervals. Nontrivial estimates for some of these mean values are given. As application inter alia, we show that for large odd n ¬ 1 ( 6 ) , Goldbach’s ternary problem n = p 1 + p 2 + p 3 is solvable with primes p 1 , p 2 in short intervals p i [ X i , X i + Y ] with X i θ i = Y , i = 1 , 2 , and θ 1 , θ 2 0 . 933 such that ( p 1 + 2 ) ( p 2 + 2 ) has at most 9 prime factors.

Infinite families of noncototients

A. Flammenkamp, F. Luca (2000)

Colloquium Mathematicae

For any positive integer n let ϕ(n) be the Euler function of n. A positive integer n is called a noncototient if the equation x-ϕ(x)=n has no solution x. In this note, we give a sufficient condition on a positive integer k such that the geometrical progression ( 2 m k ) m 1 consists entirely of noncototients. We then use computations to detect seven such positive integers k.

Large sets with small doubling modulo p are well covered by an arithmetic progression

Oriol Serra, Gilles Zémor (2009)

Annales de l’institut Fourier

We prove that there is a small but fixed positive integer ϵ such that for every prime p larger than a fixed integer, every subset S of the integers modulo p which satisfies | 2 S | ( 2 + ϵ ) | S | and 2 ( | 2 S | ) - 2 | S | + 3 p is contained in an arithmetic progression of length | 2 S | - | S | + 1 . This is the first result of this nature which places no unnecessary restrictions on the size of S .

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