Find n-th pair of prime numbers with a difference of two in MATLAB

find_prime_pair.m

n = 90;

disp(primePair(n))
function p = primePair(n)
    % Incredibly inefficient, use the primes vector instead.
    % I just came up with this during an exam and didn't want
    % to think about going over the vector correctly too much.
    a = [ -2 0 ];
    counter = 0;
    while counter ~= n
        a(1) = a(1) + 1;
        a(2) = a(2) + 1;
        % isprime(a(2)) gets checked first. If it fails,
        % it won't proceed to run isprime(a(1)), which will
        % fail initially, as a(1) is a negative number.
        %
        % This could be worked around with the abs() function
        % but I really gotta hand in this test and only have 54 minutes.
        if isprime(a(2)) && isprime(a(1))
            counter = counter + 1;
        end
    end
    p = a;
end