<div id="acctCode1">
<input class="entity" id="Entities1_0_" name="Entities1[0]" type="text" value="788" /><br/>
<input class="entity" id="Entities1_1_" name="Entities1[1]" type="text" value="Q83" /><br/>
<input class="entity" id="Entities1_2_" name="Entities1[2]" type="text" value="" /><br/>
</div>

var ent1 = new List<string>();
for (int i = 0; i < ent1.Count; i++)
{
    var entKey = "Entities1[" + i.ToString() + "]";
    var acct = Request.Form[entKey];
    if (!string.IsNullOrEmpty(acct))
    {
        ent1.Add(acct);
    }
    else
    {
        break;
    }
}