49448...54321 (147-digits)

This number is a prime.

                                                                     4944844
7446445444 4434424414 4043933833 7336335334 3333323313 3032922822 7226225224
2232222212 2021911811 7116115114 1131121111 1019988776 6554433221 1987654321

The smallest googol prime formed by concatenating in descending order the first n palindromic numbers (case n=56). [Gupta]