The CAS Registry Mumber 1121-36-4 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,1,2 and 1 respectively; the second part has 2 digits, 3 and 6 respectively. Calculate Digit Verification of CAS Registry Number 1121-36: (6*1)+(5*1)+(4*2)+(3*1)+(2*3)+(1*6)=34 34 % 10 = 4 So 1121-36-4 is a valid CAS Registry Number.