If the initial term of an arithmetic progression is *a* and the common difference of successive members is *d*, then the *n*-th term of the sequence is given by

*a*+*nd*,*n*= 0, 1, 2, ... if the initial term is taken as the 0th*a*+ (*n*-1)*d*,*n*= 1, 2, ... if the initial term is taken as the 1st

The sum of the numbers in an arithmetic progression is called an arithmetic series. A convenient formula for arithmetic series is available.

See also geometric progression.