The CAS Registry Mumber 8001-18-1 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 8,0,0 and 1 respectively; the second part has 2 digits, 1 and 8 respectively. Calculate Digit Verification of CAS Registry Number 8001-18: (6*8)+(5*0)+(4*0)+(3*1)+(2*1)+(1*8)=61 61 % 10 = 1 So 8001-18-1 is a valid CAS Registry Number.