The square root of number 121 is "11". What is the square root of number "12345678987654321." ?

Square Root 12345678987654321 Puzzle

111111111

It is a very popular square root series i.e.
Square root fo number 121 is 11
Square root fo number 12321 is 111
Square root fo number 1234321 is 1111 and so on....

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