Arithmetic progression's formula:

Tolerance d = (an-a 1) ÷ (n- 1) (where n is greater than or equal to 2 and n is a positive integer).

Number of items = (from the last item to the first item) ÷ tolerance+1.

The last item = the first item+(item number-1) × tolerance.

The sum of the first n terms Sn = the first term ×n+ terms (number of terms-1) Tolerance /2.

The value of the nth term an = the first term+(number of terms-1) × tolerance.

The formula 2an+ 1 = an+an+2 in the arithmetic source sequence, where {an} is arithmetic progression.

Related information:

In the difference arithmetic progression, the sum of two terms with the same distance as the first two terms is equal. And is equal to the sum of the first two terms and the last two terms; In particular, if the number of terms is odd, it is equal to 2 times of the middle term, the number of terms is odd, and the sum is equal to 2 times of the middle term. See arithmetic mean term.