The CAS Registry Mumber 110661-80-8 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,1,0,6,6 and 1 respectively; the second part has 2 digits, 8 and 0 respectively. Calculate Digit Verification of CAS Registry Number 110661-80: (8*1)+(7*1)+(6*0)+(5*6)+(4*6)+(3*1)+(2*8)+(1*0)=88 88 % 10 = 8 So 110661-80-8 is a valid CAS Registry Number.