The CAS Registry Mumber 100238-66-2 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,0,2,3 and 8 respectively; the second part has 2 digits, 6 and 6 respectively. Calculate Digit Verification of CAS Registry Number 100238-66: (8*1)+(7*0)+(6*0)+(5*2)+(4*3)+(3*8)+(2*6)+(1*6)=72 72 % 10 = 2 So 100238-66-2 is a valid CAS Registry Number.