A sequence is a list of numbers in a specific order. Each number in the sequence is called a term. The terms in a sequence can be separated by commas and are usually represented using subscripts, such as a1, a2, a3, etc.
For arithmetic sequences:
an = a1 + (n - 1)d
Sn = n/2 * (a1 + an)
For geometric sequences:
an = a1 * r(n-1)
Sn = a1 * (1 - rn) / (1 - r)
Sequences are an important concept in mathematics and have various applications in different fields. Understanding the different types of sequences and their properties will help you solve a wide range of problems involving patterns and ordered sets of numbers.