The CAS Registry Mumber 81306-83-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,1,3,0 and 6 respectively; the second part has 2 digits, 8 and 3 respectively. Calculate Digit Verification of CAS Registry Number 81306-83: (7*8)+(6*1)+(5*3)+(4*0)+(3*6)+(2*8)+(1*3)=114 114 % 10 = 4 So 81306-83-4 is a valid CAS Registry Number.