Companies write 777 with casinos and casino apps. It is considered a lucky number in many cultures, including western culture. It is often associated with good fortune and positive energy and a sense of winning. Using 777 in the branding and marketing of casinos and casino apps is a way to attract customers and create a positive, exciting atmosphere. Additionally, the number 7 is traditionally associated with gambling and luck, so using multiple 7's (777) amplifies that association.