The CAS Registry Mumber 66277-91-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 6,6,2,7 and 7 respectively; the second part has 2 digits, 9 and 1 respectively. Calculate Digit Verification of CAS Registry Number 66277-91: (7*6)+(6*6)+(5*2)+(4*7)+(3*7)+(2*9)+(1*1)=156 156 % 10 = 6 So 66277-91-6 is a valid CAS Registry Number.