The CAS Registry Mumber 6191-88-4 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 6,1,9 and 1 respectively; the second part has 2 digits, 8 and 8 respectively. Calculate Digit Verification of CAS Registry Number 6191-88: (6*6)+(5*1)+(4*9)+(3*1)+(2*8)+(1*8)=104 104 % 10 = 4 So 6191-88-4 is a valid CAS Registry Number.