Sum of Factors of Factors

Create a function that takes a number and returns the sum of factors of factors of the given number.

Examples

sum_ff(69) ➞ 3, 23 ➞ 0
# Both 3 and 23 are prime numbers and have no factors
# other than 1 and themselves so the result is 0.

sum_ff(12) ➞ 2, 3, 4, 6 ➞ (0) + (0) + (2) + (2+3) ➞ 7

sum_ff(420) ➞ 2,4, 6, 10, 12 ... ➞ (2) + (2+3) + (2+5) + (2+3+4+6) ... ➞ 1175

sum_ff(619) ➞ ___ ➞ 0
# 619 doesn't have any factors (other than 1 and 619).

Notes

• The number will always be greater than 0.
• Factors that are equal to the number or 1, don't count (see example #1).