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Questions where prime numbers play a key-role, such as: questions on the distribution of prime numbers (twin primes, gaps between primes, Hardy–Littlewood conjectures, etc); questions on prime numbers with special properties (Wieferich prime, Wolstenholme prime, etc.). This tag is often used as a specialized tag in combination with the top-level tag nt.number-theory and (if applicable) analytic-number-theory.

3 votes
1 answer
417 views

Primes from arithmetic and geometric progressions

The five primes, 131, 157, 211, 349, 739, are neither in arithmetic or geometric progression, but are instead the sum of the five corresponding terms of an arithmetic and geometric progression. Are …
Bernardo Recamán Santos's user avatar
5 votes
2 answers
309 views

Pairs of integers whose product is one more or less than a prime

Given a positive integer N it is often possible to pair each of the integers 1, 2, 3, ..., N with a different integer between N + 1 and 2 N so that the product of each pair is one less or more than a …
Bernardo Recamán Santos's user avatar
2 votes
1 answer
740 views

Is every prime greater than 5, less than the sum of the two previous primes?

Can one prove by elementary means (such as Paul Erdös' proof of Bertrand's Postulate) that every prime greater than 5 is less than the sum of the two primes immediately preceding it?
Bernardo Recamán Santos's user avatar
5 votes
2 answers
483 views

Least (and largest) possible number of non-relatively prime pairs among consecutive integers

Given a set of positive integers consider the graph whose vertices are those integers, two of which are joined by an edge if and only if they have a common divisor greater than 1 (i.e, they are not re …
Bernardo Recamán Santos's user avatar
8 votes
4 answers
591 views

Covering the primes with pairs of consecutive integers

Is it true that for every sufficiently large positive integer $n$, one can always find at most $k=\lfloor\pi(n)/2\rfloor$ integers, $a_1,a_2,a_3,a_3,\dots a_k$, between $1$ and $n$, such that each of …
Bernardo Recamán Santos's user avatar
3 votes
0 answers
84 views

Are numbers which are the product of n primes more common than numbers which are the product... [duplicate]

In a recent video (https://www.facebook.com/188916357807416/videos/519169035700435/) Stephen Wolfram wonders whether, for every integer n>2, eventually the number of integers which are precisely the p …
Bernardo Recamán Santos's user avatar
16 votes
3 answers
2k views

Are 0 and 1, respectively, the least and most used digits among primes?

In order to write the first 25 primes (2 to 97), 46 digits are necessary, nine of each of the digits 2, 3, and 7, fewer of all the others. Thereafter, at least for a while, the digit 1 is used more ti …
Bernardo Recamán Santos's user avatar
11 votes
1 answer
466 views

Perfect Runs of Consecutive Integers

A run of 2 or more consecutive integers is said to be perfect if the sum of its terms equals the sum of all the their proper divisors, adding common divisors as often as they occur. For example, 672, …
Bernardo Recamán Santos's user avatar
2 votes
1 answer
174 views

Graceful graphs all of whose vertices are labelled with primes or squares

Do graceful graphs exist with more than any arbitrarily large number of vertices, all of which are labelled with a prime or non-negative square number. Recall that a graceful graph is a graph with m …
Bernardo Recamán Santos's user avatar
7 votes
0 answers
545 views

Is every integer greater than 1 the sum of a palindrome and a prime?

Helfgott proved that any odd number greater than 5 is the sum of three primes. Cilleruelo and Luca proved that every positive integer is the sum of three palindromes. Is every integer greater than 1 …
Bernardo Recamán Santos's user avatar