The sum of the terms of a sequence is called a series . If a sequence is arithmetic or geometric there are formulas to find the sum of the first n terms, denoted Sn , without actually adding all of the terms.
Therefore the factors of 21 are 1, 3, 7 and 21. All that is left to do is to work out the sum of these numbers, that is to add them all up. 21+1 + 3 +7 = 32Therefore, the sum of the factors of 21 is 32.
In mathematics, sum can be defined as the result or answer we get on adding two or more numbers or terms. Here, for example, addends 8 and 5 add up to make the sum 13. The sum of the opposite sides of a die is always seven.
Summary: Adding two positive integers always yields a positive sum; adding two negative integers always yields a negative sum. To find the sum of a positive and a negative integer, take the absolute value of each integer and then subtract these values.