Bitcoin excludes a few normal characters for the sake of readability, and a Bitcoin address can be either 33 or 34 characters long. It's:
1[1-9A-HJ-NP-Za-km-z]{32,33}
Incorrect. The smallest valid BitCoin address is
1111111111111111111114oLvT2
so the addresses can go down to 27 characters. Also, 34 character BitCoin addresses can't start with "1R" "1S" "1T" etc...
I also have the ability to generate useful novelty BitCoin addresses. The best one for me so far is
1ByteCosnsUNJun4KL3HSt1NfFdXpzoRTy (pesky s)
ByteCoin
I have a couple bitcoin addresses that start with 1R, but they are very rare compared to the others. Same with 1S, 1T, etc.. Actually
Starting from 1R, all the way to 1Y, 1Z, 1a, 1b, 1c, .., 1x, 1y, 1z - these are all very rare but still they can exist.