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Euler problem #25

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May 5, 2008, 11:48:26 AM5/5/08

|What is the first term in the Fibonacci sequence to contain 1000 digits?

They only want the index.

I used the formula of Moivre-Binet (and ignored the (1/phi)^n part):

5e fsqrt 1e f+ 2e f/ fconstant phi
999e 5e fsqrt flog f+ phi flog f/ f>d 1. d+ d.

Quite short compared to some of the stuff posted in the forum.

The 1. D+ is there to simulate rounding up (we don't want the last
term below, but the first term above).

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