The CAS Registry Mumber 20853-61-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,0,8,5 and 3 respectively; the second part has 2 digits, 6 and 1 respectively. Calculate Digit Verification of CAS Registry Number 20853-61: (7*2)+(6*0)+(5*8)+(4*5)+(3*3)+(2*6)+(1*1)=96 96 % 10 = 6 So 20853-61-6 is a valid CAS Registry Number.