The CAS Registry Mumber 1273-81-0 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,2,7 and 3 respectively; the second part has 2 digits, 8 and 1 respectively. Calculate Digit Verification of CAS Registry Number 1273-81: (6*1)+(5*2)+(4*7)+(3*3)+(2*8)+(1*1)=70 70 % 10 = 0 So 1273-81-0 is a valid CAS Registry Number.