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Task/Truncatable-primes/EchoLisp/truncatable-primes-1.echolisp

@@ -0,0 +1,16 @@
+;; does p include a 0 in its decimal representation ?
+(define (nozero? n) (= -1 (string-index (number->string n) "0")))
+
+;; right truncate : p and successive quotients by 10 (integer division) must be primes
+(define (right-trunc p) (unless (zero? p)
+	(and (prime? p) (right-trunc (quotient p 10)))))
+(remember 'right-trunc)
+
+;; left truncate : p and successive modulo by 10, 100, .. must be prime
+(define (left-trunc p (mod 1000000))
+	(unless (< mod 1)
+	(and (prime? p) (nozero? p) (left-trunc (modulo p mod) (/ mod 10)))))
+
+;; start from 999999. stop on first found
+(define (fact-trunc trunc)
+(for ((p (in-range 999999 100000 -1))) #:break (when (trunc p) (writeln p) #t)))

Task/Truncatable-primes/EchoLisp/truncatable-primes-2.echolisp

@@ -0,0 +1,4 @@
+(fact-trunc left-trunc)
+998443
+(fact-trunc right-trunc)
+739399