The CAS Registry Mumber 74131-28-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,4,1,3 and 1 respectively; the second part has 2 digits, 2 and 8 respectively. Calculate Digit Verification of CAS Registry Number 74131-28: (7*7)+(6*4)+(5*1)+(4*3)+(3*1)+(2*2)+(1*8)=105 105 % 10 = 5 So 74131-28-5 is a valid CAS Registry Number.