The CAS Registry Mumber 10535-42-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,0,5,3 and 5 respectively; the second part has 2 digits, 4 and 2 respectively. Calculate Digit Verification of CAS Registry Number 10535-42: (7*1)+(6*0)+(5*5)+(4*3)+(3*5)+(2*4)+(1*2)=69 69 % 10 = 9 So 10535-42-9 is a valid CAS Registry Number.