The CAS Registry Mumber 127421-53-8 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,7,4,2 and 1 respectively; the second part has 2 digits, 5 and 3 respectively. Calculate Digit Verification of CAS Registry Number 127421-53: (8*1)+(7*2)+(6*7)+(5*4)+(4*2)+(3*1)+(2*5)+(1*3)=108 108 % 10 = 8 So 127421-53-8 is a valid CAS Registry Number.