# 2015 Countdown Problem #16: Some Brute Force & Luck Needed – Part I

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 $$n≥2$$.

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

#GoodLuckHaveFun

This problem is part of the set 2015 Countdown Problems.

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