They are important in summability theory. He is known for his work in number theory and summability. A variety of general results concerning possible summability methods are known. Note that (B) summability for formula 42 depends on the nature of the point. Let formula 2 be a summability kernel, and formula 20 denote the convolution operation. Summability conditions are discussed in detail in Boas & Buck. Since then, mathematicians have explored many different summability methods for divergent series. In the mathematics of convergent and divergent series, Euler summation is a summability method. In mathematical analysis, Lambert summation is a summability method for a class of divergent series.