In mathematics, the term Beurling algebra is used for different algebras introduced by Arne Beurling, usually it is an algebra of periodic functions with Fourier series f = ∑ a n e i n x {\displaystyle f=\sum a_{n}e^{inx}} Example We may consider the algebra of those functions f where the majorants c k = sup | n | ≥ k | a n | {\displaystyle c_{k}=\sup _{|n|\geq k}|a_{n}|} of the Fourier coefficients an are summable. Wikipedia