The CAS Registry Mumber 128231-41-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,8,2,3 and 1 respectively; the second part has 2 digits, 4 and 1 respectively. Calculate Digit Verification of CAS Registry Number 128231-41: (8*1)+(7*2)+(6*8)+(5*2)+(4*3)+(3*1)+(2*4)+(1*1)=104 104 % 10 = 4 So 128231-41-4 is a valid CAS Registry Number.