11111...11111 (271-digits)

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

         1 1111111111 0001110001 1111111111 0001110001 1111111111 0001110001
1111111111 0001110001 1111111111 0001110001 1111111111 0001110001 1111111111
0001110001 1111111111 0001110001 1111111111 0001110001 1111111111 0001110001
1111111111 0001110001 1111111111 0001110001 1111111111 0001110001 1111111111

(((10^11-1)/9)*10^20+111*10^14)*(10^(13*20)-1)/((10^20-1)/1)+((10^11-1)/9) is a "tetradic super-palindromic prime" with many lines of symmetry. [Stath]