# Multiples of N

## Find a sum of following arithmatic series

2 + 4 + 6 + 8 + ⋯ + 50


### Solving a problem

For instance, to abbreviate the writing of the series 2+4+6+8+⋯+50. Consider following:

2⋅1 + 2⋅2 + 2⋅3 + 2⋅4 + ⋯ + 2⋅25


We can easily say that it follows series 2n. The series begins with the term for n=1 and ends with the term for n=25.

A series can be written in an abbreviated form by using the Greek letter ∑(sigma), called the summation sign.

Using sigma notation, you can write this series as

= 2⋅1 + 2⋅2 + 2⋅3 + 2⋅4 + ⋯ + 2⋅25

= 2 + 4 + 6 + 8 + ⋯ + 50