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+ The first 65 digits of 6565 form a prime number. [Honaker]

+ 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 ac - 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 pi(65) = pi(5) * pi(13) = 5 + 13. [Honaker]

+ The smallest Fermat semiprime. [Capelle]

+ pi(65) = phi(65) - 6*5. [Langroudi]

(There is one curio for this number that has not yet been approved by an editor.)




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