The CAS Registry Mumber 1171920-11-8 includes 10 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 7 digits, 1,1,7,1,9,2 and 0 respectively; the second part has 2 digits, 1 and 1 respectively. Calculate Digit Verification of CAS Registry Number 1171920-11: (9*1)+(8*1)+(7*7)+(6*1)+(5*9)+(4*2)+(3*0)+(2*1)+(1*1)=128 128 % 10 = 8 So 1171920-11-8 is a valid CAS Registry Number.