The CAS Registry Mumber 135583-74-3 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 4 respectively. Calculate Digit Verification of CAS Registry Number 135583-74: (8*1)+(7*3)+(6*5)+(5*5)+(4*8)+(3*3)+(2*7)+(1*4)=143 143 % 10 = 3 So 135583-74-3 is a valid CAS Registry Number.