12196...99243 (57-digits)

This number is a prime.

              1219683 8531441159 4323177147 4782969173 7659049561 2218799243

1
13
139
12739
1281739
1281739243
1281737299243
12817372218799243
128173765612218799243
12196838173765612218799243
1219683817376590495612218799243
1219683817714717376590495612218799243
1219683853144117714717376590495612218799243
12196838531441159432317714717376590495612218799243
121968385314411594323177147478296917376590495612218799243

Beginning at 1 and successively inserting the powers of 3 we may form a pyramid of 'powers of 3 deletable primes.' This prime is the largest obtained in the above chain. [Rupinski]