The CAS Registry Mumber 6206-57-1 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 6,2,0 and 6 respectively; the second part has 2 digits, 5 and 7 respectively. Calculate Digit Verification of CAS Registry Number 6206-57: (6*6)+(5*2)+(4*0)+(3*6)+(2*5)+(1*7)=81 81 % 10 = 1 So 6206-57-1 is a valid CAS Registry Number.