The CAS Registry Mumber 82103-83-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,2,1,0 and 3 respectively; the second part has 2 digits, 8 and 3 respectively. Calculate Digit Verification of CAS Registry Number 82103-83: (7*8)+(6*2)+(5*1)+(4*0)+(3*3)+(2*8)+(1*3)=101 101 % 10 = 1 So 82103-83-1 is a valid CAS Registry Number.