16 lines
649 B
Common Lisp
16 lines
649 B
Common Lisp
(defun fermat-number (n)
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"Return the n-th Fermat number"
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(1+ (expt 2 (expt 2 n))) )
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(defun factor (n &optional (acc '()))
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"Return the list of factors of n"
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(when (> n 1) (loop with max-d = (isqrt n)
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for d = 2 then (if (evenp d) (1+ d) (+ d 2)) do
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(cond ((> d max-d) (return (cons (list n 1) acc)))
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((zerop (rem n d))
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(return (factor (truncate n d) (if (eq d (caar acc))
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(cons
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(list (caar acc) (1+ (cadar acc)))
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(cdr acc))
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(cons (list d 1) acc)))))))))
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