There are three steps in calculating friendly numbers:If two numbers have the same abundancy, then they are called Friendly Numbers.

- Find the list of all factors (even non prime) of a number.
- Find the sum of all those factors.
- Divide the sum of all the factors by that number itself.

- List of all factors is: 1, 2, 3, 5, 6, 10, 15, 30
- Sum of all factors is: 1 + 2 + 3 + 5 + 6 + 10 + 15 + 30 = 72
- Divide 72 by 30, so we get 12/5.

**abundancy****of the number 30.**

Again, we repeat:

140 has the same abundancy (= 12/5) as 30, and therefore 140 and 30 are called friendly numbers.If two numbers have the same abundancy, then they are called Friendly Numbers.

Calculating the abundancy of 140:

- List of all factors of 140: 1, 2, 4, 5, 7, 10, 14, 20, 28, 35, 70, 140
- Sum of all factors: 1 + 2 + 4 + 5 + 7 + 10 + 14 + 20 + 28 + 35 + 70 + 140 = 336
- Divide 336 by 140, so we get 12/5.

**Friendly Numbers**.

*Similarly, all other numbers which have the same abundancy are called friendly numbers.\*

### List of Friendly Numbers (first 20)

(6, 28), (30, 140), (80, 200), (40, 224), (12, 234), (84, 270), (66, 308), (78, 364), (102, 476), (6, 496), (28, 496), (114, 532), (240, 600), (138, 644), (120, 672), (150, 700), (174, 812), (135, 819), (186, 868), (864, 936), (222, 1036), (246, 1148)

Sweet

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