This paper describes practical programming with types parameterized by numbers: e.g., an array type parameterized by the array's size or a modular group type Zn parameterized by the modulus. An attempt to add, for example, two integers of different moduli should result in a compile-time error with a clear error message. Number-parameterized types let the programmer capture more invariants through types and eliminate some run-time checks. Oleg shows several approaches towards encoding numbers into types and using those numbers to check list length, matching sizes for matrices or vectors. Oleg also points out connections to dependent types, phantom types, and shape-invariant programming.