The CAS Registry Mumber 56221-16-0 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 5,6,2,2 and 1 respectively; the second part has 2 digits, 1 and 6 respectively. Calculate Digit Verification of CAS Registry Number 56221-16: (7*5)+(6*6)+(5*2)+(4*2)+(3*1)+(2*1)+(1*6)=100 100 % 10 = 0 So 56221-16-0 is a valid CAS Registry Number.