7 is the integer the proceeds 6 and precedes 8. 7 is a Mersenne prime and a Woodall prime. To check if a number is divisible by 7, double the last digit of the number and subtract the result from the original number without the last digit, repeat this process if needed. If the final result is divisible by 7, then the original number is also divisible by 7. Seven is a Happy Number.
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