1997 and 1999 form a twin prime pair.
The 1997 substrings 199 and 997 are also primes (A069489).
1997 remains a prime when a single digit 9 is inserted between any two consecutive digits or as the leading or trailing digit (A215421).
1997 is a prime factor of 87654321.
1997 has a representation as a sum of two squares: 1997 = 292 + 342.
1997 is the hypotenuse of a primitive Pythagorean triple: 19972 = 3152 + 19722.
Source: What's Special About This Number?
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