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The product of the first two primes of the form 4n + 1.

Euler found 65 integers, which he called "numeri idonei", that could be used to prove the primality of certain numbers. [Brown]

6⁶⁵ - 5 is the smallest prime of the form a^c - b, where b = a - 1. Note that c is the concatenation of a and b. [Kulsha]

The smallest composite number of the form n² + 1, where n is even.

65 is the ONLY number which gives a prime square, on adding as well as subtracting its reverse from it (65 + 56 = 11², 65 - 56 = 3²). [Gupta]

The only number which is the difference of fourth powers of two primes. [Murthy]

(65!)² + 1 is prime. [Dobb]

65 = 5 * 13 and (65) = (5) * (13) = 5 + 13. [Honaker]

The smallest Fermat semiprime. [Capelle]