What is the nth term of 9 11 13 15 17?

The sequence is simply achieved by adding 2 to each value

1. 9+2=11
2. 11+2=13
3. 13+2=15
4. 15+2=17
5. 17+2=19
6. 19+2=21

so the nth term can be calculated

The value of the nth term = the value of (nth-1 term) +2.