22 lines
643 B
Racket
22 lines
643 B
Racket
#lang racket
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(require math/number-theory)
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(define (primefactors x)
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(if (prime? x)
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(list x)
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(for/or ((i (cons 2 (range 3 (+ 1 (ceiling (sqrt x))) 2)))
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#:when (prime? i)
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#:when (zero? (remainder x i)))
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(cons i (primefactors (quotient x i))))))
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(define (recur x)
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(if (and
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(equal? (length (remove-duplicates (primefactors x))) 4)
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(equal? (length (remove-duplicates (primefactors (+ x 1)))) 4)
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(equal? (length (remove-duplicates (primefactors (+ x 2)))) 4)
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(equal? (length (remove-duplicates (primefactors (+ x 3)))) 4))
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x
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(recur (+ x 1))))
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(recur 2) |