The CAS Registry Mumber 135509-75-0 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,5,5,0 and 9 respectively; the second part has 2 digits, 7 and 5 respectively. Calculate Digit Verification of CAS Registry Number 135509-75: (8*1)+(7*3)+(6*5)+(5*5)+(4*0)+(3*9)+(2*7)+(1*5)=130 130 % 10 = 0 So 135509-75-0 is a valid CAS Registry Number.