The CAS Registry Mumber 100438-36-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,0,4,3 and 8 respectively; the second part has 2 digits, 3 and 6 respectively. Calculate Digit Verification of CAS Registry Number 100438-36: (8*1)+(7*0)+(6*0)+(5*4)+(4*3)+(3*8)+(2*3)+(1*6)=76 76 % 10 = 6 So 100438-36-6 is a valid CAS Registry Number.