Might be useful:
What is a Sequence?
A Sequence is a list of things (usually numbers) that are in order.
Sequence 3,5,7,9,…
Infinite or Finite
When the sequence goes on forever it is called an infinite sequence,
otherwise it is a finite sequence
Examples:
{1, 2, 3, 4, …} is a very simple sequence (and it is an infinite sequence)
{20, 25, 30, 35, …} is also an infinite sequence
{1, 3, 5, 7} is the sequence of the first 4 odd numbers (and is a finite sequence)
{4, 3, 2, 1} is 4 to 1 backwards
{1, 2, 4, 8, 16, 32, …} is an infinite sequence where every term doubles
{a, b, c, d, e} is the sequence of the first 5 letters alphabetically
{f, r, e, d} is the sequence of letters in the name "fred"
{0, 1, 0, 1, 0, 1, …} is the sequence of alternating 0s and 1s (yes they are in order, it is an alternating order in this case)
In Order
When we say the terms are "in order", we are free to define what order that is! They could go forwards, backwards … or they could alternate … or any type of order we want!
Like a Set
A Sequence is like a Set, except:
the terms are in order (with Sets the order does not matter)
the same value can appear many times (only once in Sets)
Example: {0, 1, 0, 1, 0, 1, …} is the sequence of alternating 0s and 1s.
The set is just {0,1}
Notation
Sequences also use the same notation a sets:
list each element, separated by a comma,
and then put curly brackets around the whole thing. {3, 5, 7, …}
The curly brackets { } are sometimes called "set brackets" or "braces".
A great resource for Anons seeking very simple refresher (or a friendly first exposure) in Sequences and Sets is: Mathisfun.com