The CAS Registry Mumber 75840-66-3 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,5,8,4 and 0 respectively; the second part has 2 digits, 6 and 6 respectively. Calculate Digit Verification of CAS Registry Number 75840-66: (7*7)+(6*5)+(5*8)+(4*4)+(3*0)+(2*6)+(1*6)=153 153 % 10 = 3 So 75840-66-3 is a valid CAS Registry Number.