12345...54321 (849-digits)

This number is a probable-prime (likely to be a prime but we have not (re-)proven it on this site).

The largest non-titanic palindromic prime of the form 1234567891*10^(k + 10) + 1987654321 (for k = 829), where k is the number of zeros between 1234567891 and 1987654321. [Gupta]