The CAS Registry Mumber 424-31-7 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 4,2 and 4 respectively; the second part has 2 digits, 3 and 1 respectively. Calculate Digit Verification of CAS Registry Number 424-31: (5*4)+(4*2)+(3*4)+(2*3)+(1*1)=47 47 % 10 = 7 So 424-31-7 is a valid CAS Registry Number.