The CAS Registry Mumber 173909-83-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,7,3,9,0 and 9 respectively; the second part has 2 digits, 8 and 3 respectively. Calculate Digit Verification of CAS Registry Number 173909-83: (8*1)+(7*7)+(6*3)+(5*9)+(4*0)+(3*9)+(2*8)+(1*3)=166 166 % 10 = 6 So 173909-83-6 is a valid CAS Registry Number.