The CAS Registry Mumber 77169-09-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,7,1,6 and 9 respectively; the second part has 2 digits, 0 and 9 respectively. Calculate Digit Verification of CAS Registry Number 77169-09: (7*7)+(6*7)+(5*1)+(4*6)+(3*9)+(2*0)+(1*9)=156 156 % 10 = 6 So 77169-09-6 is a valid CAS Registry Number.