The CAS Registry Mumber 181770-72-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,8,1,7,7 and 0 respectively; the second part has 2 digits, 7 and 2 respectively. Calculate Digit Verification of CAS Registry Number 181770-72: (8*1)+(7*8)+(6*1)+(5*7)+(4*7)+(3*0)+(2*7)+(1*2)=149 149 % 10 = 9 So 181770-72-9 is a valid CAS Registry Number.