The CAS Registry Mumber 4994-91-6 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 4,9,9 and 4 respectively; the second part has 2 digits, 9 and 1 respectively. Calculate Digit Verification of CAS Registry Number 4994-91: (6*4)+(5*9)+(4*9)+(3*4)+(2*9)+(1*1)=136 136 % 10 = 6 So 4994-91-6 is a valid CAS Registry Number.