The CAS Registry Mumber 113521-11-2 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,1,3,5,2 and 1 respectively; the second part has 2 digits, 1 and 1 respectively. Calculate Digit Verification of CAS Registry Number 113521-11: (8*1)+(7*1)+(6*3)+(5*5)+(4*2)+(3*1)+(2*1)+(1*1)=72 72 % 10 = 2 So 113521-11-2 is a valid CAS Registry Number.