The CAS Registry Mumber 6239-81-2 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 6,2,3 and 9 respectively; the second part has 2 digits, 8 and 1 respectively. Calculate Digit Verification of CAS Registry Number 6239-81: (6*6)+(5*2)+(4*3)+(3*9)+(2*8)+(1*1)=102 102 % 10 = 2 So 6239-81-2 is a valid CAS Registry Number.