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]