The CAS Registry Mumber 921-84-6 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 9,2 and 1 respectively; the second part has 2 digits, 8 and 4 respectively. Calculate Digit Verification of CAS Registry Number 921-84: (5*9)+(4*2)+(3*1)+(2*8)+(1*4)=76 76 % 10 = 6 So 921-84-6 is a valid CAS Registry Number.