The CAS Registry Mumber 27491-99-2 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,7,4,9 and 1 respectively; the second part has 2 digits, 9 and 9 respectively. Calculate Digit Verification of CAS Registry Number 27491-99: (7*2)+(6*7)+(5*4)+(4*9)+(3*1)+(2*9)+(1*9)=142 142 % 10 = 2 So 27491-99-2 is a valid CAS Registry Number.