The CAS Registry Mumber 126683-81-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,6,6,8 and 3 respectively; the second part has 2 digits, 8 and 1 respectively. Calculate Digit Verification of CAS Registry Number 126683-81: (8*1)+(7*2)+(6*6)+(5*6)+(4*8)+(3*3)+(2*8)+(1*1)=146 146 % 10 = 6 So 126683-81-6 is a valid CAS Registry Number.