factors: classifying numbers.

factors/factors.factor

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+! Copyright (C) 2011 John Benediktsson.
+! See http://factorcode.org/license.txt for BSD license.
+
+USING: kernel math math.functions math.ranges math.vectors
+sequences sets ;
+
+IN: factors
+
+: factor? ( m n -- ? )
+    mod zero? ;
+
+: factors ( n -- seq )
+    dup [1,b] [ factor? ] with filter ;
+
+: factors' ( n -- seq )
+    dup sqrt ceiling >integer factors
+    [ n/v ] keep append members ;
+
+: check-factors ( n quot: ( m n -- ? ) -- ? )
+    [ [ factors sum ] [ - ] ] dip tri ; inline
+
+: perfect? ( n -- ? ) [ = ] check-factors ;
+
+: abundant? ( n -- ? ) [ > ] check-factors ;
+
+: deficient? ( n -- ? ) [ < ] check-factors ;