89

This number is a prime.

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Hugo Steinhaus (1887-1972) proved that if you take any positive integer, find the sum of the squares of its digits, and then repeat; that you will either come to 1 or the cyclic sequence 145, 42, 20, 4, 16, 37, 58, 89.

Submitted: 2003-01-26 19:01:25;   Last Modified: 2009-01-17 09:55:33.
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