Why is it called 53 bank?

Ashton State Bank 2 BANCFIRST 15 Bank of Grand Lake 1 Community Banking Company 6 DALLAS CAP Bank National Association 1 First Bank of Boaz 6 FIRST MW Bank OF THE OZARKS 14 First National Bank in DeRidder 5 First National Bank of Carmi 4 JONESTOWN B&TC OF JONESTOWN PA 21 KLEBERG Bank National Association 4 Ledyard National Bank 7 MEDALLION Bank 18 SAGE CAP Bank 9 Security Bank of Southwest Missouri 5 SmartBiz Bank, National Association 7 State Bank of Faribault 14 Twin River Bank 4 UNION Bank CO 20 WEST Bank 30