# method 1: ((
(( n=10 ))
(( n = n + 10 ))
(( n = $n + 10 ))
a=$(( 2*100+1 ))

# method 2: let
let "z=5*3"
let "z = 5 * 4"
let "z=5	*3"
let "z=z+1"
let "z=$z+1"
let "z++"

# method 3: expr
expr 37 + 2    # space required
expr 37 \* 2
expr 37 / 2
expr 37 % 2
expr length "a_string"
 
# operators
+ - * / 	* %
	* is the exponentiation
+= -= *= /= %=
    let "var += 5"

# decompose an integer into prime factors.
$ factor 27417
27417: 3 13 19 37

References

• http://www.linuxtopia.org/online_books/advanced_bash_scripting_guide/ops.html