The CAS Registry Mumber 23213-34-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,3,2,1 and 3 respectively; the second part has 2 digits, 3 and 4 respectively. Calculate Digit Verification of CAS Registry Number 23213-34: (7*2)+(6*3)+(5*2)+(4*1)+(3*3)+(2*3)+(1*4)=65 65 % 10 = 5 So 23213-34-5 is a valid CAS Registry Number.