A sequence, also called a progression, is an ordered set of numbers (e.g., 2, 4, 6, 8, ...2n, ...), which may be finite or infinite in length. The members of the sequence are linked by a common mathematical formula. Infinite sequences may or may not be convergent (tend to a single limit). The sequence 0, 0.9, 0.99, 0.999, ... for example is convergent, tending to the limit 1. Among the different types of sequence are arithmetic sequences, geometric sequences, and harmonic sequences.
A unimodal sequence is a sequence that first increases and then decreases.