The CAS Registry Mumber 91021-22-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,1,0,2 and 1 respectively; the second part has 2 digits, 2 and 2 respectively. Calculate Digit Verification of CAS Registry Number 91021-22: (7*9)+(6*1)+(5*0)+(4*2)+(3*1)+(2*2)+(1*2)=86 86 % 10 = 6 So 91021-22-6 is a valid CAS Registry Number.