$ cat build.xml 
<project name="Attachments" default="print">
    <property name="numAttachments" value="20" />
    <target name="generate">
        <script language="javascript"><![CDATA[
            var list = '1';
            var limit = project.getProperty( "numAttachments" );
            for (var i=2;i<limit;i++)
            { 
                list = list + ',' + i;
            }
            project.setNewProperty("list", list);            
		print(list);
        ]] >
        </script>    
    </target>
</project>

		
		

		
$ ant generate
Buildfile: /www/testing/build.xml

generate:
   [script] 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19

BUILD SUCCESSFUL
Total time: 0 seconds