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Oppermann's Conjecture

open

Posed by Ludvig Oppermann · analytic number theory · ~1 min read · difficulty 4/5

prime-gaps

The problem

For every integer \(n > 1\) there is at least one prime \(p\) with \(n(n-1) < p < n^2\) and at least one prime \(q\) with \(n^2 < q < n(n+1)\). In particular there is always a prime between consecutive squares, so Oppermann's conjecture implies Legendre's.

History & significance

Formulated by the Danish mathematician, actuary and politician Ludvig Oppermann in the late 19th century. It sharpens Legendre's conjecture from one prime per square-interval to one in each half: the intervals \([n(n-1), n^2]\) and \([n^2, n(n+1)]\) each contain a prime. Like its siblings it is computationally confirmed far beyond doubt but theoretically open; Cramér's probabilistic model predicts it comfortably, and any proof would have to beat the Baker–Harman–Pintz exponent substantially.

Still open.

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