The CAS Registry Mumber 135303-84-3 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,5,3,0 and 3 respectively; the second part has 2 digits, 8 and 4 respectively. Calculate Digit Verification of CAS Registry Number 135303-84: (8*1)+(7*3)+(6*5)+(5*3)+(4*0)+(3*3)+(2*8)+(1*4)=103 103 % 10 = 3 So 135303-84-3 is a valid CAS Registry Number.