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

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