The CAS Registry Mumber 211677-17-7 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 2,1,1,6,7 and 7 respectively; the second part has 2 digits, 1 and 7 respectively. Calculate Digit Verification of CAS Registry Number 211677-17: (8*2)+(7*1)+(6*1)+(5*6)+(4*7)+(3*7)+(2*1)+(1*7)=117 117 % 10 = 7 So 211677-17-7 is a valid CAS Registry Number.