The CAS Registry Mumber 3213-18-1 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 3,2,1 and 3 respectively; the second part has 2 digits, 1 and 8 respectively. Calculate Digit Verification of CAS Registry Number 3213-18: (6*3)+(5*2)+(4*1)+(3*3)+(2*1)+(1*8)=51 51 % 10 = 1 So 3213-18-1 is a valid CAS Registry Number.