33333...33333 (4261-digits)

This number is a prime.

Let R(n)=(10^n-1)/9 be the n-digit base-10 repunit. As of June 2003, the 4261-digit number (30*R(15)+4)*R(4260)/R(15)-1 was the largest known palindromic prime with prime digits. Proof: http://groups.yahoo.com/group/primeform/message/3390 [Broadhurst]