1 and 3 are the common prefixes.

1 is most common and denotes a simple "pay-to-PubKey" transaction. This transaction shows an actual recipient address.

3 indicates a "pay-to-script-hash" address that contains a hash (one way fingerprint) of a script that can be used for multiple things including address obfuscation and multi-signature requirements. This script is required to be a valid bitcoin transaction script, but the full script behind the scenes is not public, just the hash.

More information here: https://en.bitcoin.it/wiki/BIP_0016

1 and 3 are currently the only defined prefixes for an base58 encoded address.

1 is most common and denotes a simple "pay-to-PubKey" transaction. This transaction shows an actual recipient address.

3 indicates a "pay-to-script-hash" address that contains a hash (one way fingerprint) of a script that can be used for multiple things including address obfuscation and multi-signature requirements. This script is required to be a valid bitcoin transaction script, but the full script behind the scenes is not public, just the hash.

More information here: https://en.bitcoin.it/wiki/BIP_0016

More info on the base58 implementation used: https://en.bitcoin.it/wiki/Base58Check_encoding