The CAS Registry Mumber 1807-61-0 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,8,0 and 7 respectively; the second part has 2 digits, 6 and 1 respectively. Calculate Digit Verification of CAS Registry Number 1807-61: (6*1)+(5*8)+(4*0)+(3*7)+(2*6)+(1*1)=80 80 % 10 = 0 So 1807-61-0 is a valid CAS Registry Number.