19

This number is a prime.

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19 is the largest prime factor of 1444 - the smallest perfect square to end in three 4's. Note that 4 is the only non-zero digit that can repeat at the end of a perfect square, and the most consecutive 4's that can appear in such a place is three. [Litman]

Submitted: 2004-01-30 02:06:25; Last Modified: 2008-01-30 17:28:00.