77777...54321 (238-digits)

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

                                              77777776 6666665555 5554444444
3333333222 2222111111 1999999888 8887777776 6666655555 5444444333 3332222221
1111199999 8888877777 6666655555 4444433333 2222211111 9999888877 7766665555
4444333322 2211119998 8877766655 5444333222 1119988776 6554433221 1987654321

The smallest prime that is reverse concatenation of first n positive repdigit numbers, (case n=61). [Bajpai]