The CAS Registry Mumber 1812-61-9 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,8,1 and 2 respectively; the second part has 2 digits, 6 and 1 respectively. Calculate Digit Verification of CAS Registry Number 1812-61: (6*1)+(5*8)+(4*1)+(3*2)+(2*6)+(1*1)=69 69 % 10 = 9 So 1812-61-9 is a valid CAS Registry Number.