An arithmetic series is given by:
Tn = a + (n-1)d, where Tn is the nth term, a is the first term, n is a positive integer, and d is the 'common difference' - how much the series is increasing by. An example is:
2, 4, 6, 8, 10, etc.
This is written as Tn = 2 + (n-1)2 - it is increasing...