The CAS Registry Mumber 135191-28-5 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,5,1,9 and 1 respectively; the second part has 2 digits, 2 and 8 respectively. Calculate Digit Verification of CAS Registry Number 135191-28: (8*1)+(7*3)+(6*5)+(5*1)+(4*9)+(3*1)+(2*2)+(1*8)=115 115 % 10 = 5 So 135191-28-5 is a valid CAS Registry Number.