The CAS Registry Mumber 81685-30-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,1,6,8 and 5 respectively; the second part has 2 digits, 3 and 0 respectively. Calculate Digit Verification of CAS Registry Number 81685-30: (7*8)+(6*1)+(5*6)+(4*8)+(3*5)+(2*3)+(1*0)=145 145 % 10 = 5 So 81685-30-5 is a valid CAS Registry Number.