Source code in the pl/i programming language

mertens: procedure options(main);
    %replace MAX by 1000;
    
    declare M(1:MAX) fixed binary(5);
    declare (n, k) fixed binary(10);
    declare (isZero, crossZero) fixed binary(8);
    
    M(1) = 1;
    do n = 2 to MAX;
        M(n) = 1;
        do k = 2 to n;
            M(n) = M(n) - M(divide(n,k,10));
        end;
    end;
    
    put skip list('The first 99 Mertens numbers are:');
    put skip list('   ');
    do n = 1 to 99;
        put edit(M(n)) (F(3));
        if mod(n,10) = 9 then put skip;
    end;
    
    isZero = 0;
    crossZero = 0;
    do n = 2 to MAX;
        if M(n) = 0 then do;
            isZero = isZero + 1;
            if M(n-1) ^= 0 then
                crossZero = crossZero + 1;
        end;
    end;
    
    put skip list('Zeroes:   ',isZero); 
    put skip list('Crossings:',crossZero);
end mertens;