The CAS Registry Mumber 83138-28-7 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,3,1,3 and 8 respectively; the second part has 2 digits, 2 and 8 respectively. Calculate Digit Verification of CAS Registry Number 83138-28: (7*8)+(6*3)+(5*1)+(4*3)+(3*8)+(2*2)+(1*8)=127 127 % 10 = 7 So 83138-28-7 is a valid CAS Registry Number.