All mainstream credit card numbers obey a mathematical trick designed to catch the most common typos. It’s called the Luhn algorithm, named after IBM researcher Hans Peter Luhn, who patented it in ...

Jason Fernando is a professional investor and writer who enjoys tackling and communicating complex business and financial problems. Khadija Khartit is a strategy, investment, and funding expert, and ...

You’re at the checkout screen after an online shopping spree, ready to enter your credit card number. You type it in and instantly see a red error message ...