Result

jQuery

    $('li').each(function(index){
        //3つごとに設定
        if(Math.floor(index/3)%2==0){
        //classを付加
            $(this).css('color','blue');
        }else{
            $(this).css('color','red');
        };
        });

html

<ul>
<li>list01</li>
<li>list02</li>
　　　・
　　　・
　　　・
<li>list14</li>
<li>list15</li>
<li>list16</li>
</ul>

via

How to target list items per two lists instead of even or odd – Stack Overflow

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