20000...00031 (91-digits)

This number is a prime.

                                                     2 0000312000 0322000033
2000035200 0036200003 7200003820 0003720000 3620000352 0000332000 0322000031

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The smallest prime formed from the concatenation of n consecutive n-digit uban numbers in the pattern {a, b, c, d, e, f, g, f, e, d, c, b, a}, i.e., {2000031, 2000032, 2000033, 2000035, 2000036, 2000037, 2000038, 2000037, 2000036, 2000035, 2000033, 2000032, 2000031}, (case n=7). [Bajpai]