The CAS Registry Mumber 74121-72-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,4,1,2 and 1 respectively; the second part has 2 digits, 7 and 2 respectively. Calculate Digit Verification of CAS Registry Number 74121-72: (7*7)+(6*4)+(5*1)+(4*2)+(3*1)+(2*7)+(1*2)=105 105 % 10 = 5 So 74121-72-5 is a valid CAS Registry Number.