New posts in Divisor Sum

What's the sum of all the positive integral divisors of $540$?

The sigma function (sum of divisors) multiplicative proof

What is the sum of all positive even divisors of 1000?

Find two-digit numbers such that their ratio equals $0.254902$.

Show that $\sum\nolimits_{d|n} \frac{1}{d} = \frac{\sigma (n)}{n}$ for every positive integer $n$.