The CAS Registry Mumber 165619-89-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,6,5,6,1 and 9 respectively; the second part has 2 digits, 8 and 9 respectively. Calculate Digit Verification of CAS Registry Number 165619-89: (8*1)+(7*6)+(6*5)+(5*6)+(4*1)+(3*9)+(2*8)+(1*9)=166 166 % 10 = 6 So 165619-89-6 is a valid CAS Registry Number.