The CAS Registry Mumber 72221-72-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,2,2,2 and 1 respectively; the second part has 2 digits, 7 and 2 respectively. Calculate Digit Verification of CAS Registry Number 72221-72: (7*7)+(6*2)+(5*2)+(4*2)+(3*1)+(2*7)+(1*2)=98 98 % 10 = 8 So 72221-72-8 is a valid CAS Registry Number.