The CAS Registry Mumber 74993-61-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,4,9,9 and 3 respectively; the second part has 2 digits, 6 and 1 respectively. Calculate Digit Verification of CAS Registry Number 74993-61: (7*7)+(6*4)+(5*9)+(4*9)+(3*3)+(2*6)+(1*1)=176 176 % 10 = 6 So 74993-61-6 is a valid CAS Registry Number.