The divisors of 30 are 1, 2, 3, 5, 6, 10, 15, and 30. Add those up and divide the sum by 30 itself and you get 12/5.

The divisors of 140 are 1, 2, 4, 5, 7, 10, 14, 20, 28, 35, 70, and 140. Add those up and divide the sum by 140 and you also get 12/5.

This makes 30 and 140 a friendly pair. Other members of their little club are 2480, 6200, and 40640.

Interestingly, no one knows whether 10 has such a partner. If it does, its smallest friend is at least 10³⁰.