14 lines
510 B
Common Lisp
14 lines
510 B
Common Lisp
(defun attractivep (n)
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(primep (length (factors n))) )
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; For primality testing we can use different methods, but since we have to define factors that's what we'll use
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(defun primep (n)
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(= (length (factors n)) 1) )
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(defun factors (n)
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"Return a list of factors of N."
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(when (> n 1)
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(loop with max-d = (isqrt n)
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for d = 2 then (if (evenp d) (+ d 1) (+ d 2)) do
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(cond ((> d max-d) (return (list n))) ; n is prime
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((zerop (rem n d)) (return (cons d (factors (truncate n d)))))))))
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