Giuga numbers: Difference between revisions

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 858 1722 66198</lang>
-These numbers have some interesting properties but there's an issue with guaranteeing correctness of more sophisticated approaches.
+These numbers have some interesting properties but there's an issue with guaranteeing correctness of more sophisticated approaches. That said, here's a translation of the pari/gp implementation on the talk page:
+<lang J>divisors=: [: /:~@, */&>@{@((^ i.@>:)&.>/)@q:~&__
+giuga=: {{
+  r=. i.0
+  p=. (2) 0 1} s=. 1r2,}.(2>.y-1+t=.1)$0
+  while. t do.
+    p=. p t}~ 4 p:t{p
+    s=. s t}~ (s{~t-1)+1%t{p
+    if. (1=t{s) +. 1 >: (t{s)+(y-t+1)%t{p do.
+      t=. t-1
+    elseif. t<y-3 do.
+      p=. p (t+1)}~ (p{~t) >. (%-.)s{~t
+      t=. t+1
+    else.
+      'c d'=. 2 x: s{~y-3
+      dc=. d-c
+      k=. (d^2)-dc
+      for_h. ({.~ <.@-:@>:@#) f=. divisors k do.
+        if. 0=dc|h+d do.
+          if. 0=dc|dkh=. d+k%h do.
+            py3=. p{~y-3
+            if. py3 < r1=. (h+d)%dc do.
+              if. py3 < r2=. dkh%dc do.
+                if. r1~:r2 do.
+                  if. 1 p: r1 do.
+                    if. 1 p: r2 do.
+                      r=. r, d*r1*r2
+                    end.
+                  end.
+                end.
+              end.
+            end.
+          end.
+        end.
+      end.
+    end.
+  end.
+  r
+}}</lang>
+Example use:<lang J>   giuga 1
+   giuga 2
+   giuga 3
+   giuga 4
+858
+   giuga 5
+   giuga 6
+24423128562 2214408306</lang>
 =={{header|Julia}}==