The CAS Registry Mumber 216373-63-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 2,1,6,3,7 and 3 respectively; the second part has 2 digits, 6 and 3 respectively. Calculate Digit Verification of CAS Registry Number 216373-63: (8*2)+(7*1)+(6*6)+(5*3)+(4*7)+(3*3)+(2*6)+(1*3)=126 126 % 10 = 6 So 216373-63-6 is a valid CAS Registry Number.