Number of possible outcome for tossing N coins = 
Solution:
Possible outcomes when tossing one coin = {H, T}
Number of possible outcomes when tossing one coin = 2 
Possible outcomes when tossing two coins = {HH, HT, TH, TT}
Number of possible outcomes when tossing two coins = 4 
Possible outcomes when tossing three coins
= {HHH, HHT, HTH, THH, TTH, THT, HTT, TTT}
Number of possible outcomes when tossing three coins = 8 
Therefore, the sequence obtained is
.
If continue this sequence, we can obtain number of possible outcome for tossing N coins is
.