June 2018 Update

Task/Truncatable-primes/Ring/truncatable-primes.ring

@@ -0,0 +1,56 @@
+# Project : Truncatable primes
+# Date    : 2017/10/15
+# Author : Gal Zsolt (~ CalmoSoft ~)
+# Email   : <calmosoft@gmail.com>
+
+for n = 1000000 to 1 step -1
+    flag = 1
+    flag2 = 1
+    strn = string(n)
+    for nr = 1 to len(strn)
+        if strn[nr] = "0"
+           flag2 = 0
+        ok
+    next
+    if flag2 = 1
+       for m = 1 to len(strn)
+           strp = right(strn, m)
+           if isprime(number(strp))
+           else
+              flag = 0
+              exit
+           ok
+       next
+       if flag = 1
+          nend = n
+          exit
+       ok
+    ok
+next
+see "Largest left truncatable prime : " + nend + nl
+
+for n = 1000000 to 1 step -1
+    flag = 1
+    strn = string(n)
+    for m = 1 to len(strn)
+        strp = left(strn, len(strn) - m + 1)
+        if isprime(number(strp))
+        else
+           flag = 0
+           exit
+        ok
+    next
+    if flag = 1
+       nend = n
+       exit
+    ok
+next
+see "Largest right truncatable prime : " + nend + nl
+
+func isprime num
+     if (num <= 1) return 0 ok
+     if (num % 2 = 0 and num != 2) return 0 ok
+     for i = 3 to floor(num / 2) -1 step 2
+         if (num % i = 0) return 0 ok
+     next
+     return 1