Kummer's congruence

The simplest form of Kummer's congruence states that

${\displaystyle {\frac {B_{h}}{h}}\equiv {\frac {B_{k}}{k}}{\pmod {p}}{\text{ whenever }}h\equiv k{\pmod {p-1}}}$

where p is a prime, h and k are positive even integers not divisible by p−1 and the numbers B_h are Bernoulli numbers.

More generally if h and k are positive even integers not divisible by p − 1, then

${\displaystyle (1-p^{h-1}){\frac {B_{h}}{h}}\equiv (1-p^{k-1}){\frac {B_{k}}{k}}{\pmod {p^{a+1}}}}$

whenever

${\displaystyle h\equiv k{\pmod {\varphi (p^{a+1})}}}$

where φ(p^a+1) is the Euler totient function, evaluated at p^a+1 and a is a non negative integer. At a = 0, the expression takes the simpler form, as seen above. The two sides of the Kummer congruence are essentially values of the p-adic zeta function, and the Kummer congruences imply that the p-adic zeta function for negative integers is continuous, so can be extended by continuity to all p-adic integers.

• Von Staudt–Clausen theorem, another congruence involving Bernoulli numbers

• Koblitz, Neal (1984), p-adic Numbers, p-adic Analysis, and Zeta-Functions, Graduate Texts in Mathematics, vol. 58, Berlin, New York: Springer-Verlag, ISBN 978-0-387-96017-3, MR 0754003
• Kubota, Tomio; Leopoldt, Heinrich-Wolfgang (1964), "Eine p-adische Theorie der Zetawerte. I. Einführung der p-adischen Dirichletschen L-Funktionen", Journal für die reine und angewandte Mathematik, 214/215: 328–339, doi:10.1515/crll.1964.214-215.328, ISSN 0075-4102, MR 0163900
• Kummer, Ernst Eduard (1851), "Über eine allgemeine Eigenschaft der rationalen Entwicklungscoëfficienten einer bestimmten Gattung analytischer Functionen", Journal für die Reine und Angewandte Mathematik, 41: 368–372, doi:10.1515/crll.1851.41.368, ISSN 0075-4102, ERAM 041.1136cj