The CAS Registry Mumber 79918-31-3 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,9,9,1 and 8 respectively; the second part has 2 digits, 3 and 1 respectively. Calculate Digit Verification of CAS Registry Number 79918-31: (7*7)+(6*9)+(5*9)+(4*1)+(3*8)+(2*3)+(1*1)=183 183 % 10 = 3 So 79918-31-3 is a valid CAS Registry Number.