How are you with patterns?

For as long as I can remember, I've been fascinated by all manner of codes and patterns. When I sent some out at the end of a recent newsletter, I was thrilled by the number of people who engaged with the puzzles and doubly impressed by how many people got them right.
If you want to have a go, add your answers in a comment below.

Give me the next 2 in each of these sequences:

a)  2, 5, 8, 11, __ , __

b)  2, 5, 10, 17, __ , __

c)  j, f, m, a, _ , _

Good luck. I will be giving the answers some time in the next week.
The third one is a little tricksy - if you want a clue, scroll down.































Part c) is do do with time, it's not (exactly) a numerical sequence.