Using Java

class MyCalculator implements AdvancedArithmetic{

@Override

public int divisor_sum(int n) { int sum=0; for(int i=1;i<=n;i++) { if(n%i==0) sum += i;

    }
    return sum;
}

}

You can optimize by going only up to sqrt(n) and adding both the factors at once (similar principal when looking for Prime numbers).

    public int divisor_sum(int n) {
        if(n==1) return 1;
        int sum=0;
        for(int i=1; i * i <= n; i++) {
            if(n%i==0) {
                sum += i;
                sum += n/i; //other factor of a * b = n
            }
        }
        return sum;
    }

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Here is java Interface solution - https://programmingoneonone.com/hackerrank-java-interface-problem-solution.html

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