The CAS Registry Mumber 791-66-2 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 7,9 and 1 respectively; the second part has 2 digits, 6 and 6 respectively. Calculate Digit Verification of CAS Registry Number 791-66: (5*7)+(4*9)+(3*1)+(2*6)+(1*6)=92 92 % 10 = 2 So 791-66-2 is a valid CAS Registry Number.