The CAS Registry Mumber 166249-05-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,6,6,2,4 and 9 respectively; the second part has 2 digits, 0 and 5 respectively. Calculate Digit Verification of CAS Registry Number 166249-05: (8*1)+(7*6)+(6*6)+(5*2)+(4*4)+(3*9)+(2*0)+(1*5)=144 144 % 10 = 4 So 166249-05-4 is a valid CAS Registry Number.