fn card_at(chars: &[char], start: usize) -> Option<(usize, String)>Expand description
A payment card number, Luhn’s check digit right: 16 or 19 digits from a network’s first digit (2 to 6), or 15 from American Express’s 34 and 37. Fourteen digits are left alone: a SIRET has a Luhn key too, and is no secret.