Problem 197
Investigating the behaviour of a recursively defined sequence

Given is the function f(x) = ⌊230.403243784-x2⌋× 10-9 ( ⌊⌋ is the floor-function),
the sequence un is defined by u0 = -1 and un+1 = f(un).

Find un + un+1 for n = 1012.
Give your answer with 9 digits after the decimal point.

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http://projecteuler.net/problem=197