The CAS Registry Mumber 108161-11-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,8,1,6 and 1 respectively; the second part has 2 digits, 1 and 1 respectively. Calculate Digit Verification of CAS Registry Number 108161-11: (8*1)+(7*0)+(6*8)+(5*1)+(4*6)+(3*1)+(2*1)+(1*1)=91 91 % 10 = 1 So 108161-11-1 is a valid CAS Registry Number.