the arithmetic sequence is a common sequence. if the difference between each item in a sequence starting from the second item and its previous item is equal to the same constant, the sequence is called an arithmetic sequence, and this constant is called an arithmetic sequence. the tolerance is usually represented by the letter d. for example: 1,3,5,7,9...1+2(n-1).

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