An arithmetic sequence is a common sequence. If the difference between each term and the previous term of a sequence starting from the second term is equal to the same constant, this sequence is called an arithmetic sequence, and this constant is called the common difference of the arithmetic sequence, which is usually represented by the letter d. For example: 1,3,5,7,9...1+2(n-1).

The general formula of an arithmetic sequence is: an=a1+(n-1)d (1) The sum of the first n terms is: or Sn=n(a1+an)/2. Note: All n above are positive integers.