The CAS Registry Mumber 428-18-2 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 4,2 and 8 respectively; the second part has 2 digits, 1 and 8 respectively. Calculate Digit Verification of CAS Registry Number 428-18: (5*4)+(4*2)+(3*8)+(2*1)+(1*8)=62 62 % 10 = 2 So 428-18-2 is a valid CAS Registry Number.