The CAS Registry Mumber 42108-41-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 4,2,1,0 and 8 respectively; the second part has 2 digits, 4 and 1 respectively. Calculate Digit Verification of CAS Registry Number 42108-41: (7*4)+(6*2)+(5*1)+(4*0)+(3*8)+(2*4)+(1*1)=78 78 % 10 = 8 So 42108-41-8 is a valid CAS Registry Number.