The CAS Registry Mumber 128671-29-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,8,6,7 and 1 respectively; the second part has 2 digits, 2 and 9 respectively. Calculate Digit Verification of CAS Registry Number 128671-29: (8*1)+(7*2)+(6*8)+(5*6)+(4*7)+(3*1)+(2*2)+(1*9)=144 144 % 10 = 4 So 128671-29-4 is a valid CAS Registry Number.