Here i is the divisor of j and we are trying to add the sum of multiplication of all triplets of divisors of j such that one of the divisors is i
for ( $ i = 1 ; $ i < $ max_Element ; $ i ++ ) for ( $ j = $ i ; $ j < $ max_Element ; $ j += $ i ) $ sum3 [ $ j ] += $ i * ( $ sum2 [ $ j ] - $ i * ( $ sum1 [ $ j ] - $ i ) ) ;