10

This number is a composite.

The only known number n such that the forms n+R(n), n^2+R(n^2), 3^n+2, 3^(R(n))+2 are all primes, where R(n) is the reversal of n, i.e., 10+01=11, 100+001=101, 3^10+2=59051, 3^01+2=5. [Loungrides]