The difference between the first two numbers is 117-113 = 4
The difference between the third and the second number is 126-117=9
The difference between the fourth and the third number is 151-126=25
The difference between the fifth and the fourth number is 200-151=49

We can see that all the differences are squares of the prime numbers. 
The next difference would be the square of the next prime number, $$11^2=121$$
making the sixth number of the series to be 200+121 = 321

Therefore, Option C is the correct answer.