2719
This number is a prime.
In 1917, Ramanujan gave a short list of odd numbers which cannot be written as x2 + y2 + 10z2. Eighty years later it is was shown that 2719 is surely the largest such number (GRH). Did you notice 2719 is a permutation of the Hardy-Ramanujan number? [Ono1997] [Beedassy]
(There are 2 curios for this number that have not yet been approved by an editor.)
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