matlab loops break and continue commands

In number theory, a semi-perfect number is a positive integer number that is equal to the sum of its largest three positive divisors, excluding the number itself. For example; 18 is a semiperfect number, the positive divisors of this number are 1,2,3,6,9,18, and the sum of the three largest integer divisors (excluding the number itself) is 3 + 6 + 9 = 18. Write a MATLAB program that checks whether a given number is semi-perfect number.

[Ameer Hamza]

This seems like a homework question. What have you already tried?

[mehmet kiraccakali]

n=input('Enter a number ');
sum=0;
for i=n-1:-1:1
    if mod(n,i)==0
  sum=sum+i;
    end
end
  if sum==n
      fprintf('%d is a semi-perfect number \n',n);
  else
      fprintf('%d is not a semi-perfect number \n',n);
  end

I couldn't solve this question either, I tried to make the solution above. but i don't know how to find the three biggest divisors.

Answer 1

[Peng Li]

You are almost there. Just need a seperate counter that force the loop to break if it accumulates to 3.

n   = input('Enter a number ');
sum = 0;
ind = 0;
for i = n-1:-1:1
    if mod(n, i) == 0
        sum = sum + i;
        ind = ind + 1;
        
        if ind == 3
            break;
        end
    end
end
if sum == n
    fprintf('%d is a semi-perfect number \n',n);
else
    fprintf('%d is not a semi-perfect number \n',n);
end

[mehmet kiraccakali]

thank you so much

[Ayberk Dönmez]

write a matlab program that calculates the sum of the largest positive divisor (excluding itself) and the smallest positive divisor (excluding 1) of a given number? do you have any idea about this question ?

[Peng Li]

You can keep doing your way of using a loop; store all divisors found; and do a min/max after that.

A better work around:

n = input('Enter a number ');
k = 2:ceil(n/2);       % you don't need to search through bigger numbers, as they won't be a divisor anyway
d = k(rem(n, k) == 0); % you get all divisors

if isempty(d)
    disp('no divisors found except the number itself and 1');
else
    yourNeedResult = d(1) + d(end);
    fprintf("the largest positve divisor (excluding itself) of %d is %d\r", n, d(end));
    fprintf("the smallest positive divisor (excluding 1) of %d is %d\r", n, d(1));
    fprintf("there sum is %d\r", d(1)+d(end));
end
Enter a number 18
the largest positve divisor (excluding itself) of 18 is 9
the smallest positive divisor (excluding 1) of 18 is 2
there sum is 11

[Walter Roberson]

Hint: mod(number, potential_factor)

[Gamze Elmastas]

What is the mean of if ind==3? I dont know the mean of ind.

[Ayberk Dönmez]

thank you so much

[Walter Roberson]

sum of its largest three positive divisors

That is why 3 was chosen to compare against.

ind is being used to count how many factors have been found so far.