The CAS Registry Mumber 72867-21-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,2,8,6 and 7 respectively; the second part has 2 digits, 2 and 1 respectively. Calculate Digit Verification of CAS Registry Number 72867-21: (7*7)+(6*2)+(5*8)+(4*6)+(3*7)+(2*2)+(1*1)=151 151 % 10 = 1 So 72867-21-1 is a valid CAS Registry Number.