7 7 18 a`````` `a````` ``a```` ```a``` ``````` ``````` ``````` a`````` `a````` ``a```` ```b``` ``````` ``````` ``````` a`````` `a````` ``a```` ``b```` ``````` ``````` ``````` a`````` `a````` `ba```` ``````` ``````` ``````` ``````` a`````` `a````` ``b```` ```b``` ``````` ``````` ``````` a`````` `a````` ``b```` ```c``` ``````` ``````` ``````` a`````` `a````` ``b```` ``c```` ``````` ``````` ``````` a`````` `a````` ``b```` `b````` ``````` ``````` ``````` a`````` `a````` ``b```` `c````` ``````` ``````` ``````` a`````` `a````` `cb```` ``````` ``````` ``````` ``````` a`````` ba````` ``b```` ``````` ``````` ``````` ``````` a`````` ca````` ``b```` ``````` ``````` ``````` ``````` a`````` `a````` `b````` b`````` ``````` ``````` ``````` a`````` `a````` cb````` ``````` ``````` ``````` ``````` a`````` `ac```` `b````` ``````` ``````` ``````` ``````` a`````` ba````` `b````` ``````` ``````` ``````` ``````` ab````` ba````` ``````` ``````` ``````` ``````` ``````` a`````` `b````` ``c```` ```d``` ``````` ``````` ``````` Found 18 different among 98 A complete list.