The CAS Registry Mumber 129587-21-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,9,5,8 and 7 respectively; the second part has 2 digits, 2 and 1 respectively. Calculate Digit Verification of CAS Registry Number 129587-21: (8*1)+(7*2)+(6*9)+(5*5)+(4*8)+(3*7)+(2*2)+(1*1)=159 159 % 10 = 9 So 129587-21-9 is a valid CAS Registry Number.