9973

This number is a prime.

+ The largest prime less than ten thousand; additionally, on deleting the last digit, it becomes the largest prime less than one thousand. [Hasler]

+ The largest 4-digit prime whose sum of digits is a perfect number. [Loungrides]

+ The only 4-digit prime formed from the concatenation of two primes summed to a thousand, (997, 3). [Loungrides]

+ The largest prime number that has the same number of digits as its prime index which is also a prime number (1229). [Gaydos]

+ The largest 4-digit prime 9973 can be read as “99 is the 73rd composite number.” [Loungrides]

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