18181...18181 (77-digits)

This number is a prime.

                                                                     1818181
8181818181 8181818181 8181818181 8181818181 8181818181 8181818181 8181818181

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A smoothly undulating tedradic palindromic prime which is (7*11) digits in length and has a sum of digits equal to 7^3. Note that the difference between the two digits it uses equals 7. [Necula]