The CAS Registry Mumber 5274-66-8 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 5,2,7 and 4 respectively; the second part has 2 digits, 6 and 6 respectively. Calculate Digit Verification of CAS Registry Number 5274-66: (6*5)+(5*2)+(4*7)+(3*4)+(2*6)+(1*6)=98 98 % 10 = 8 So 5274-66-8 is a valid CAS Registry Number.