Question 634781
The sequence is 


2,4,6,8,10,...


since you're adding 2 to each number to get the next number.


So on the 5th night, 10 people are bitten. Add up all the numbers from 2 to 10 in that list to get 2+4+6+8+10 = 30


Don't forget to add the original vampire that started everything to get 30+1 = <font color="red">31 total vampires</font> on the fifth night.