The CAS Registry Mumber 127399-17-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,7,3,9 and 9 respectively; the second part has 2 digits, 1 and 7 respectively. Calculate Digit Verification of CAS Registry Number 127399-17: (8*1)+(7*2)+(6*7)+(5*3)+(4*9)+(3*9)+(2*1)+(1*7)=151 151 % 10 = 1 So 127399-17-1 is a valid CAS Registry Number.