Bitcoin wallet addresses are case sensitive, usually have 34 characters of numbers and lowercase letters, start with either a 1 or a 3, and never use 0, O, l and I to make every character in the address as clear as possible. Disclaimer: Buy Bitcoin Worldwide is not offering, promoting, or encouraging the purchase, sale, or trade of any security or commodity. The same goes for Kraken, Poloniex, or any other exchange or service that holds your coins! Mycelium is the most popular Bitcoin wallet on Android.