The CAS Registry Mumber 7166-44-1 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 7,1,6 and 6 respectively; the second part has 2 digits, 4 and 4 respectively. Calculate Digit Verification of CAS Registry Number 7166-44: (6*7)+(5*1)+(4*6)+(3*6)+(2*4)+(1*4)=101 101 % 10 = 1 So 7166-44-1 is a valid CAS Registry Number.