29 lines
608 B
Racket
29 lines
608 B
Racket
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#lang racket
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(require math/number-theory)
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(define σ
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(let ((memo (make-hash)))
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(λ (z)
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(hash-ref! memo z
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(λ () (apply + (divisors z)))))))
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(define p
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(let ((memo (make-hash '((0 . 1)))))
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(λ (n)
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(hash-ref!
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memo n
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(λ ()
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(let ((r (if (zero? n) 1
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(/ (for/sum ((k (in-range (sub1 n) -1 -1)))
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(* (σ (- n k))
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(p k)))
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n))))
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(when (zero? (modulo n 1000)) (displayln (cons n r) (current-error-port)))
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r))))))
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(map p (range 1 30))
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(p 666)
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(p 1000)
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(p 10000)
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