The CAS Registry Mumber 3884-97-7 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 4 respectively; the second part has 2 digits, 9 and 7 respectively. Calculate Digit Verification of CAS Registry Number 3884-97: (6*3)+(5*8)+(4*8)+(3*4)+(2*9)+(1*7)=127 127 % 10 = 7 So 3884-97-7 is a valid CAS Registry Number.