Sequential Circuits - No of flip flops required

Question

If there are total 16 different states in a system and there is one external input, then how many flip flops are required? Is it 3 or 4 ?

Thank you.

Comments

Note that all counters are not self starting counters(especially ring and twisted ring counters), you need external i/p

in case of ripple counters, if you didn't use external i/p then counter always starts with either 0 ( by default ) or last

but if you want your sequence from some point, then external inputs required.

---

what is meaning of external input.

---

it is nothing but initial input from user.