[交流] 欧拉工程，第二十一题，计算10000以下亲和数的和。 已有5人参与

function result = euler21()
tic;
result = [];
for i=1:10000
    if d(i)~=i && d(d(i))==i
        result = [result,i];
    end
end
result = sum(unique(result));
toc;
end

%% Let d(n) denote the sum of proper divisors of n (numbers less than n which divide evenly into n).
% For example, the proper divisors of 220 are 1, 2, 4, 5, 10, 11, 20, 22, 44, 55 and 110; therefore d(220) = 284.
% sub function to compute d(n), called by 21 and 23
function s = d(n)
s = 0;
for i=1:n-1
    if mod(n,i)==0
        s = s+i;
    end
end
end