Problem 21: Amicable numbers
Let d(n
) be defined as the sum of proper divisors of n
(numbers less than
n
which divide evenly into n
).
If d(a
) = b
and d(b
) = a
, where a
≠ b
, then a
and b
are an
amicable pair and each of a
and b
are called amicable numbers.
For example, the proper divisors of 220 are 1, 2, 4, 5, 10, 11, 20, 22, 44, 55 and 110; therefore d(220) = 284. The proper divisors of 284 are 1, 2, 4, 71 and 142; so d(284) = 220.
Evaluate the sum of all the amicable numbers under n
.
Test
{{test}}Console output