The CAS Registry Mumber 21966-94-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,1,9,6 and 6 respectively; the second part has 2 digits, 9 and 4 respectively. Calculate Digit Verification of CAS Registry Number 21966-94: (7*2)+(6*1)+(5*9)+(4*6)+(3*6)+(2*9)+(1*4)=129 129 % 10 = 9 So 21966-94-9 is a valid CAS Registry Number.