The CAS Registry Mumber 3891-75-6 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 3,8,9 and 1 respectively; the second part has 2 digits, 7 and 5 respectively. Calculate Digit Verification of CAS Registry Number 3891-75: (6*3)+(5*8)+(4*9)+(3*1)+(2*7)+(1*5)=116 116 % 10 = 6 So 3891-75-6 is a valid CAS Registry Number.