This is not regular becoz we need to save the count of c becoz if we put k=1 then every n times it should be 1 similarly if k=2 then every n times it should be 2.
while generating a string we will to keep the value of m,n and k
Now let us suppose m=1, n=2 and k=1
Then the string will be abcbc. That means every time c will be 1
That's why it is not regular
if k=2 and m,n remains the same then string will be abccbcc. That means everytime c will be 2
That means we will have to remmeber the count of c.