5501
This number is a prime.
Prime sum of the first five half-quartan primes (primes of
the form p = (x^4 + y^4)/2) and smallest such prime sum: 41 + 313 + 353 + 1201 + 3593 = 5501 is prime. [Post]
The sum of the first five centered hexagonal numbers
squared, i.e., 1 + 49 + 361 + 1369 + 3721 = 5501. There are
no other primes of this form. [Petrov]
(There is one curio for this number that has not yet been approved by an editor.)
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