The CAS Registry Mumber 104721-19-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,4,7,2 and 1 respectively; the second part has 2 digits, 1 and 9 respectively. Calculate Digit Verification of CAS Registry Number 104721-19: (8*1)+(7*0)+(6*4)+(5*7)+(4*2)+(3*1)+(2*1)+(1*9)=89 89 % 10 = 9 So 104721-19-9 is a valid CAS Registry Number.