The sum of the aliquot divisors of n, given by s(n) congruent σ(n) - n, where σ(n) is the divisor function. The first few values are 0, 1, 1, 3, 1, 6, 1, 7, 4, 8, 1, 16, ... (OEIS A001065).
We guarantee you’ll find the right tutor, or we’ll cover the first hour of your lesson.