Data commit

Task/Truncatable-primes/Racket/truncatable-primes.rkt

@@ -0,0 +1,32 @@
+#lang racket
+(require math/number-theory)
+
+(define (truncate-right n)
+  (quotient n 10))
+
+(define (truncate-left n)
+  (define s (number->string n))
+  (string->number (substring s 1 (string-length s))))
+
+(define (contains-zero? n)
+  (member #\0 (string->list (number->string n))))
+
+(define (truncatable? truncate n)
+  (and (prime? n)
+       (not (contains-zero? n))
+       (or (< n 10)
+           (truncatable? truncate (truncate n)))))
+
+; largest left truncatable prime
+(for/first ([n (in-range 1000000 1 -1)]
+            #:when (truncatable? truncate-left n))
+  n)
+
+; largest right truncatable prime
+(for/first ([n (in-range 1000000 1 -1)]
+            #:when (truncatable? truncate-right n))
+  n)
+
+; Output:
+998443
+739399