The CAS Registry Mumber 102131-80-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,2,1,3 and 1 respectively; the second part has 2 digits, 8 and 0 respectively. Calculate Digit Verification of CAS Registry Number 102131-80: (8*1)+(7*0)+(6*2)+(5*1)+(4*3)+(3*1)+(2*8)+(1*0)=56 56 % 10 = 6 So 102131-80-6 is a valid CAS Registry Number.