Data update

Task/M-bius-function/Forth/m-bius-function.fth

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+\ Moebius function
+: mu ( u -- n )
+  \ multiple of 4 so return 0
+  dup 3 and 0= if drop 0 exit then
+  \ even numbers have 2 as a prime factor
+  dup 1 and 0= if 2/ 1 else 0 then >r
+  \ look for odd prime factors up to the square root
+  3 begin
+    2dup dup * >=
+  while
+    2dup mod 0= if
+      tuck / swap
+      2dup mod 0= if
+        \ repeated prime factor so return 0
+        2drop rdrop 0 exit
+      then
+       \ we have another prime factor
+      r> 1+ >r
+    then
+    2 +
+  repeat
+  drop
+  \ prime factor > square root?
+  r> swap 1 > if 1+ then
+  1 and 0= if 1 else -1 then ;
+
+: main ( -- )
+  ." The first 199 Moebius numbers are:" cr
+  ."    "
+  200 1 do
+    i mu 3 .r
+    i 1+ 20 mod 0= if cr else then
+  loop ;
+
+main
+bye