Driver code
public static void main ( String [ ] args ) { StringBuilder s = new StringBuilder ( "45" ) ; System . out . println ( primeDigits ( s ) ) ; s = new StringBuilder ( "1000" ) ; System . out . println ( primeDigits ( s ) ) ; s = new StringBuilder ( "7721" ) ; System . out . println ( primeDigits ( s ) ) ; s = new StringBuilder ( "7221" ) ; System . out . println ( primeDigits ( s ) ) ; s = new StringBuilder ( "74545678912345689748593275897894708927680" ) ; System . out . println ( primeDigits ( s ) ) ; } }