The CAS Registry Mumber 81121-47-3 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,1,1,2 and 1 respectively; the second part has 2 digits, 4 and 7 respectively. Calculate Digit Verification of CAS Registry Number 81121-47: (7*8)+(6*1)+(5*1)+(4*2)+(3*1)+(2*4)+(1*7)=93 93 % 10 = 3 So 81121-47-3 is a valid CAS Registry Number.