The CAS Registry Mumber 172980-28-8 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,7,2,9,8 and 0 respectively; the second part has 2 digits, 2 and 8 respectively. Calculate Digit Verification of CAS Registry Number 172980-28: (8*1)+(7*7)+(6*2)+(5*9)+(4*8)+(3*0)+(2*2)+(1*8)=158 158 % 10 = 8 So 172980-28-8 is a valid CAS Registry Number.