This number is a prime.
Place 1 after the concatenation of the 9 digits duplicated
and obtain a 19-digit prime, whose sum of digits is the 91
appearing the end of the prime. [Silva]
(1122334455667788991, 1122334455667788997) is a sexy prime pair formed by doubling each counting digit in order and attaching at the end respectively the digits 1 and 7. [Loungrides]
(There is one curio for this number that has not yet been approved by an editor.)
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