The CAS Registry Mumber 170238-81-0 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,7,0,2,3 and 8 respectively; the second part has 2 digits, 8 and 1 respectively. Calculate Digit Verification of CAS Registry Number 170238-81: (8*1)+(7*7)+(6*0)+(5*2)+(4*3)+(3*8)+(2*8)+(1*1)=120 120 % 10 = 0 So 170238-81-0 is a valid CAS Registry Number.