The CAS Registry Mumber 74121-68-9 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, 6 and 8 respectively. Calculate Digit Verification of CAS Registry Number 74121-68: (7*7)+(6*4)+(5*1)+(4*2)+(3*1)+(2*6)+(1*8)=109 109 % 10 = 9 So 74121-68-9 is a valid CAS Registry Number.