The CAS Registry Mumber 5531-40-8 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 5,5,3 and 1 respectively; the second part has 2 digits, 4 and 0 respectively. Calculate Digit Verification of CAS Registry Number 5531-40: (6*5)+(5*5)+(4*3)+(3*1)+(2*4)+(1*0)=78 78 % 10 = 8 So 5531-40-8 is a valid CAS Registry Number.