A perfect number is a whole number (i.e. integer) which is equal in
magnitude to the sum (i.e. the result obtained by adding) of all its factors
less than itself (a factor is also known as a divisor, i.e. another whole
number that divides evenly without remainder into the number in question)
P.S. if you're wondering about the tardiness of this answer - I/we have been
away on holiday for a week - hope it's still useful!