# Schinzel's hypothesis H

In mathematics, **Schinzel's hypothesis H** is a very broad generalisation of conjectures such as the twin prime conjecture named after Andrzej Schinzel.

## Statement[edit]

The hypothesis aims to define the possible scope of a conjecture of the nature that several sequences of the type

with values at integers of irreducible integer-valued polynomials

should be able to take on prime number values simultaneously, for arbitrarily large integers . Putting it another way, there should be infinitely many such for which each of the sequence values are prime numbers. Some constraints are needed on the polynomials. Schinzel's hypothesis builds on the earlier Bunyakovsky conjecture, for a single polynomial, and on the Hardy–Littlewood conjectures and Dickson's conjecture for multiple linear polynomials. It is in turn extended by the Bateman–Horn conjecture.

Note that the coefficients of the polynomials need not to be integers; for example, this conjecture includes the polynomial , since it is an integer-valued polynomial.

## Necessary limitations[edit]

Such a conjecture requires necessary condition. For example, if we take the two polynomials and , there is no for which and are both primes. That is because one will be an even number , and the other an odd number. The main question in formulating the conjecture is to rule out this phenomenon.

Thus, we should add a condition: "For every prime *p*, there is an *n* such that all the polynomial values at *n* are not divisible by *p*".

## Fixed divisors pinned down[edit]

The arithmetic nature of the most evident necessary conditions can be understood. An integer-valued polynomial has a *fixed divisor * if there is an integer such that

is also an integer-valued polynomial. For example, we can say that

has 2 as fixed divisor. Such fixed divisors must be ruled out of

for any conjecture for polynomials , , since their presence is quickly seen to contradict the possibility that can all be prime, with large values of .

## Formulation of hypothesis H[edit]

Therefore, the standard form of **hypothesis H** is that if defined as above has *no* fixed prime divisor, then all will be simultaneously prime, infinitely often, for any choice of irreducible integral polynomials with positive leading coefficients.

If the leading coefficients were negative, we could expect negative prime values; this is a harmless restriction, really. There is probably no real reason to restrict to integral polynomials, rather than integer-valued polynomials. The condition of having no fixed prime divisor is certainly effectively checkable in a given case, since there is an explicit basis for the integer-valued polynomials. As a simple example,

has no fixed prime divisor. We therefore expect that there are infinitely many primes

This has not been proved, though. It was one of Landau's conjectures and goes back to Euler, who observed in a letter to Goldbach in 1752 that is often prime for up to 1500.

## Prospects and applications[edit]

The hypothesis is probably not accessible with current methods in analytic number theory, but is now quite often used to prove conditional results, for example in Diophantine geometry. The conjectural result being so strong in nature, it is possible that it could be shown to be too much to expect.

## Extension to include the Goldbach conjecture[edit]

The hypothesis doesn't cover Goldbach's conjecture, but a closely related version (**hypothesis H _{N}**) does. That requires an extra polynomial , which in the Goldbach problem would just be , for which

*N*−*F*(*n*)

is required to be a prime number, also. This is cited in Halberstam and Richert, *Sieve Methods*. The conjecture here takes the form of a statement *when N is sufficiently large*, and subject to the condition

*Q*(*n*)(*N*−*F*(*n*))

has *no fixed divisor* > 1. Then we should be able to require the existence of *n* such that *N* − *F*(*n*) is both positive and a prime number; and with all the *f _{i}*(

*n*) prime numbers.

Not many cases of these conjectures are known; but there is a detailed quantitative theory (Bateman–Horn conjecture).

## Local analysis[edit]

The condition of having no fixed prime divisor is purely local (depending just on primes, that is). In other words, a finite set of irreducible integer-valued polynomials
with no *local obstruction* to taking infinitely many prime values is conjectured to take infinitely many prime values.

## An analogue that fails[edit]

The analogous conjecture with the integers replaced by the one-variable polynomial ring over a finite field is *false*. For example, Swan noted in 1962 (for reasons unrelated to Hypothesis H) that the polynomial

over the ring *F*_{2}[*u*] is irreducible and has no fixed prime polynomial divisor (after all, its values at *x* = 0 and *x* = 1 are relatively prime polynomials) but all of its values as *x* runs over *F*_{2}[*u*] are composite. Similar examples can be found with *F*_{2} replaced by any finite field; the obstructions in a proper formulation of Hypothesis H over *F*[*u*], where *F* is a finite field, are no longer just *local* but a new *global* obstruction occurs with no classical parallel, assuming hypothesis H is in fact correct.

## References[edit]

- Crandall, Richard; Pomerance, Carl B. (2005).
*Prime Numbers: A Computational Perspective*(Second ed.). New York: Springer-Verlag. doi:10.1007/0-387-28979-8. ISBN 0-387-25282-7. MR 2156291. Zbl 1088.11001. - Guy, Richard K. (2004).
*Unsolved problems in number theory*(Third ed.). Springer-Verlag. ISBN 978-0-387-20860-2. Zbl 1058.11001. - Pollack, Paul (2008). "An explicit approach to hypothesis H for polynomials over a finite field". In De Koninck, Jean-Marie; Granville, Andrew; Luca, Florian (eds.).
*Anatomy of integers. Based on the CRM workshop, Montreal, Canada, March 13–17, 2006*. CRM Proceedings and Lecture Notes.**46**. Providence, RI: American Mathematical Society. pp. 259–273. ISBN 978-0-8218-4406-9. Zbl 1187.11046. - Swan, R.G. "FACTORIZATION OF POLYNOMIALS OVER FINITE FIELDS".

## External links[edit]

- [1] for the publications of the Polish mathematician Andrzej Schinzel. The hypothesis derives from paper 25 on that list, from 1958, written with Sierpiński.