The CAS Registry Mumber 171865-12-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,7,1,8,6 and 5 respectively; the second part has 2 digits, 1 and 2 respectively. Calculate Digit Verification of CAS Registry Number 171865-12: (8*1)+(7*7)+(6*1)+(5*8)+(4*6)+(3*5)+(2*1)+(1*2)=146 146 % 10 = 6 So 171865-12-6 is a valid CAS Registry Number.