The CAS Registry Mumber 686277-21-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 6,8,6,2,7 and 7 respectively; the second part has 2 digits, 2 and 1 respectively. Calculate Digit Verification of CAS Registry Number 686277-21: (8*6)+(7*8)+(6*6)+(5*2)+(4*7)+(3*7)+(2*2)+(1*1)=204 204 % 10 = 4 So 686277-21-4 is a valid CAS Registry Number.