Data commit

Task/Yellowstone-sequence/Racket/yellowstone-sequence.rkt

@@ -0,0 +1,23 @@
+#lang racket
+
+(require plot)
+
+(define a098550
+  (let ((hsh# (make-hash '((1 . 1) (2 . 2) (3 . 3))))
+        (rev# (make-hash '((1 . 1) (2 . 2) (3 . 3)))))
+    (λ (n)
+      (hash-ref hsh# n
+                (λ ()
+                  (let ((a_n (for/first ((i (in-naturals 4))
+                                         #:unless (hash-has-key? rev# i)
+                                         #:when (and (= (gcd i (a098550 (- n 1))) 1)
+                                                     (> (gcd i (a098550 (- n 2))) 1)))
+                               i)))
+                    (hash-set! hsh# n a_n)
+                    (hash-set! rev# a_n n)
+                    a_n))))))
+
+(map a098550 (range 1 (add1 30)))
+
+(plot (points
+       (map (λ (i) (vector i (a098550 i))) (range 1 (add1 100)))))