243
This number is a composite.
243 is the first number of the form pq where p & q are a prime pair (i.e., where p & q are prime and q = p + 2). [Hunter]
243 = 3^5 is the sum of three first palindromic primes: 11, 101 and 131. [Gallardo]
243 plus the product of the 243rd Fibonacci number and the 243rd Lucas number is prime. This is the largest such number less than a thousand. [Opao]
Smallest odd prime to an odd prime power, which is a sum of
distinct primorials: 243 = 4# + 3# + 1# + 0# = 210+30+2+1 =
3^5. [Post]
The first odd prime raised to the second odd prime power is
the maximum number of moves required to achieve checkmate
amongst all theoretically won chess positions with 6 pieces
on the board. [Merickel]
243^244+2 is the only non-titanic prime of form n^(n+1)+2, where n is a 3-digit number, (n=243). [Loungrides]