Utility Functions to solve Project Euler

Usage

% egison -l lib/math/project-euler.egi
> (num-to-digits 12345)
{1 2 3 4 5}
> (digits-to-num {1 2 3 4 5})
12345

> (sum-of-positive-divisors 3)
4     ; 1+3
> (sum-of-positive-divisors 12)
28    ; 1+2+3+4+6+12

> (sum-of-proper-divisors 3)
1
(sum-of-proper-divisors 12)
16    ; 1+2+3+4+6

> (num-to-digits 12345)
{1 2 3 4 5}

> (digits-to-num {1 2 3 4 5})
12345