Similar to クラメル・カスティヨンの問題

Hadamard matrix

Hadamard transform

Ackermann function

Atiyah–Singer index theorem

Sieve of Atkin

Apéry's constant

Apéry's theorem

Abel–Plana formula

Apollonius point

Apollonian gasket

Archimedes's cattle problem

Archimedean property

Twin circles

Algorithm

Artin L-function

Artin–Hasse exponential

Wedderburn–Artin theorem

Artinian module

Artinian ring

Artin–Schreier theory

Van Lamoen circle

Euler's theorem in geometry

Carnot's theorem (inradius, circumradius)

Griffiths' theorem

Kosnita's theorem

Conway circle theorem

Simson line