The CAS Registry Mumber 161646-90-8 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,6,1,6,4 and 6 respectively; the second part has 2 digits, 9 and 0 respectively. Calculate Digit Verification of CAS Registry Number 161646-90: (8*1)+(7*6)+(6*1)+(5*6)+(4*4)+(3*6)+(2*9)+(1*0)=138 138 % 10 = 8 So 161646-90-8 is a valid CAS Registry Number.