The CAS Registry Mumber 130121-16-3 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,0,1,2 and 1 respectively; the second part has 2 digits, 1 and 6 respectively. Calculate Digit Verification of CAS Registry Number 130121-16: (8*1)+(7*3)+(6*0)+(5*1)+(4*2)+(3*1)+(2*1)+(1*6)=53 53 % 10 = 3 So 130121-16-3 is a valid CAS Registry Number.