The CAS Registry Mumber 83821-90-3 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,3,8,2 and 1 respectively; the second part has 2 digits, 9 and 0 respectively. Calculate Digit Verification of CAS Registry Number 83821-90: (7*8)+(6*3)+(5*8)+(4*2)+(3*1)+(2*9)+(1*0)=143 143 % 10 = 3 So 83821-90-3 is a valid CAS Registry Number.