The CAS Registry Mumber 3886-21-3 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 3,8,8 and 6 respectively; the second part has 2 digits, 2 and 1 respectively. Calculate Digit Verification of CAS Registry Number 3886-21: (6*3)+(5*8)+(4*8)+(3*6)+(2*2)+(1*1)=113 113 % 10 = 3 So 3886-21-3 is a valid CAS Registry Number.