A formal (or analytic) series Σ a_n x^n or Σ a_n x^n/n! encoding a combinatorial sequence. Algebraic operations on series mirror combinatorial constructions (sum, product, composition).
A formal (or analytic) series Σ a_n x^n or Σ a_n x^n/n! encoding a combinatorial sequence. Algebraic operations on series mirror combinatorial constructions (sum, product, composition).