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;What is the first term in the
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;Fibonacci sequence to contain 1000 digits?
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(define (square x) (* x x))
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(define (pow man exp)
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(cond
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((= exp 0) 1)
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((< exp 0) (/ 1 (pow exp (- man))))
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((even? exp) (square (pow man (/ exp 2))))
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((odd? exp) (* man (square (pow man (/ (- exp 1) 2)))))
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(else #f)))
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(define (prob25 digits)
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(let ((big-const (pow 10 (- digits 1))))
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(let fib ((first 1) (second 1) (count 1))
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(if (>= first big-const)
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count
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(begin
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;(display first) (display " ") (display count) (newline)
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(fib second (+ first second) (+ count 1))
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)))
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)
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)
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(prob25 1000)
Tags: euler