The CAS Registry Mumber 13747-31-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,3,7,4 and 7 respectively; the second part has 2 digits, 3 and 1 respectively. Calculate Digit Verification of CAS Registry Number 13747-31: (7*1)+(6*3)+(5*7)+(4*4)+(3*7)+(2*3)+(1*1)=104 104 % 10 = 4 So 13747-31-4 is a valid CAS Registry Number.