The CAS Registry Mumber 123419-90-9 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,3,4,1 and 9 respectively; the second part has 2 digits, 9 and 0 respectively. Calculate Digit Verification of CAS Registry Number 123419-90: (8*1)+(7*2)+(6*3)+(5*4)+(4*1)+(3*9)+(2*9)+(1*0)=109 109 % 10 = 9 So 123419-90-9 is a valid CAS Registry Number.