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777 is used on most slot machines in the United States to 6️⃣ identify a jackpot. As it is considered a lucky number, banknotes with a serial number containing 777 tend to be 6️⃣ valued by collectors and numismatists. The US Mint and the Bureau of Engraving and Printing sells uncirculated 777 R$1 bills 6️⃣ for this reason.

777 (number) - Wikipedia

To play 777, follow the HOW TO WIN  instructions: Reveal a set of 6️⃣ any three like-colored "SEVEN" symbols in a row to win the corresponding prize for that row. Reveal two sets of 6️⃣ three like "SEVEN" symbols in a row to win double the prize.

777 | A Fast Play Game - Illinois Lottery