The CAS Registry Mumber 135583-75-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,5,5,8 and 3 respectively; the second part has 2 digits, 7 and 5 respectively. Calculate Digit Verification of CAS Registry Number 135583-75: (8*1)+(7*3)+(6*5)+(5*5)+(4*8)+(3*3)+(2*7)+(1*5)=144 144 % 10 = 4 So 135583-75-4 is a valid CAS Registry Number.