The CAS Registry Mumber 161404-77-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,6,1,4,0 and 4 respectively; the second part has 2 digits, 7 and 7 respectively. Calculate Digit Verification of CAS Registry Number 161404-77: (8*1)+(7*6)+(6*1)+(5*4)+(4*0)+(3*4)+(2*7)+(1*7)=109 109 % 10 = 9 So 161404-77-9 is a valid CAS Registry Number.