The CAS Registry Mumber 71939-17-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,1,9,3 and 9 respectively; the second part has 2 digits, 1 and 7 respectively. Calculate Digit Verification of CAS Registry Number 71939-17: (7*7)+(6*1)+(5*9)+(4*3)+(3*9)+(2*1)+(1*7)=148 148 % 10 = 8 So 71939-17-8 is a valid CAS Registry Number.