A CUSIP is a nine-character alphanumeric code that identifies a North American financial security for the purposes of facilitating clearing and settlement of trades.
The first six characters are known as the base (or CUSIP-6), and uniquely identify the issuer. The 7th and 8th digit identify the exact issue, the format being dependent on the type of security. The 9th digit is an automatically generated check digit using the "Modulus 10 Double Add Double" technique based on the Luhn algorithm.
037833100 931142103 14149YAR8 126650BG6 are valid,
31430F200 022615AC2 are invalid.