A number is said to be Armstrong number, if sum of the cubes of its digits is equal to the number itself.
Example: 153 = 1*1*1 + 5*5*5 + 3*3*3 = 1 + 125 + 27.
We can divide the number by 10 and get the remainder, the remainder here is also the right hand side digit. then we can divide the quotient by 10 and get the next digit. we shall do this till we get 0 as quotient. we can multiply the digit thrice by itself to get it cube.
Written with ♥ from Mangesh.