11111...11111 (23611-digits)

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

(((10^11-1)/9)*10^20+111*10^14)*(10^(1180*20)-1)/((10^20-1)/1)+((10^11-1)/9) is a "tetradic superpalindrome probable prime" with many lines of symmetry. [Stath]