The CAS Registry Mumber 128671-30-7 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, 3 and 0 respectively. Calculate Digit Verification of CAS Registry Number 128671-30: (8*1)+(7*2)+(6*8)+(5*6)+(4*7)+(3*1)+(2*3)+(1*0)=137 137 % 10 = 7 So 128671-30-7 is a valid CAS Registry Number.