The CAS Registry Mumber 110991-10-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,1,0,9,9 and 1 respectively; the second part has 2 digits, 1 and 0 respectively. Calculate Digit Verification of CAS Registry Number 110991-10: (8*1)+(7*1)+(6*0)+(5*9)+(4*9)+(3*1)+(2*1)+(1*0)=101 101 % 10 = 1 So 110991-10-1 is a valid CAS Registry Number.