2015 Countdown Problem #16: Some Brute Force & Luck Needed ā€“ Part I

Number Theory Level 4

A sequence is defined by the recurrence relation \(u_1=2015\) and \(u_n\) equals the sum of the squares of each digit in \(u_{(n-1)}\) for \(nā‰„2\).

How many more square numbers than prime numbers are there between \(u_1\) and \(u_{2015}\) inclusive?


This problem is part of the set 2015 Countdown Problems.


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