class Cusip { private static Boolean isCusip(String s) { if (s.length() != 9) return false int sum = 0 for (int i = 0; i <= 7; i++) { char c = s.charAt(i) int v if (c >= ('0' as char) && c <= ('9' as char)) { v = c - 48 } else if (c >= ('A' as char) && c <= ('Z' as char)) { v = c - 55 // lower case letters apparently invalid } else if (c == '*' as char) { v = 36 } else if (c == '@' as char) { v = 37 } else if (c == '#' as char) { v = 38 } else { return false } if (i % 2 == 1) v *= 2 // check if odd as using 0-based indexing sum += v / 10 + v % 10 } return s.charAt(8) - 48 == (10 - (sum % 10)) % 10 } static void main(String[] args) { List candidates=new ArrayList<>() candidates.add("037833100") candidates.add("17275R102") candidates.add("38259P508") candidates.add("594918104") candidates.add("68389X106") candidates.add("68389X105") for (String candidate : candidates) { System.out.printf("%s -> %s%n", candidate, isCusip(candidate) ? "correct" : "incorrect") } } }