Most likely you only have one pecan tree. Plus there a probably no other pecan trees nearby. Your pecan tree has to have another pecan tree close enough so that they can pollinate. If no pollination...
19 halves according to this link
http://leonifasufledu/fycs/newscolums/2008/pick percent 20a percent 20peck percent 20of percent 20nutritious percent 20pecanspdf?