The CAS Registry Mumber 842121-03-3 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 8,4,2,1,2 and 1 respectively; the second part has 2 digits, 0 and 3 respectively. Calculate Digit Verification of CAS Registry Number 842121-03: (8*8)+(7*4)+(6*2)+(5*1)+(4*2)+(3*1)+(2*0)+(1*3)=123 123 % 10 = 3 So 842121-03-3 is a valid CAS Registry Number.