=IF(A5<>"",MATCH(A5,A:A,0)=ROW(A5)*IF(LEN(A5)=18,MID("10X98765432",MOD(SUMPRODUCT(MID(A5,ROW(INDIRECT("1:17")),1)*2^(18-ROW(INDIRECT("1:17")))),11)+1,1)=RIGHT(A5),IF(LEN(A5)=15,ISNUMBER(--TEXT(19&MID(A5,7,6),"#-00-00")))),"")