The CAS Registry Mumber 103438-56-8 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,3,4,3 and 8 respectively; the second part has 2 digits, 5 and 6 respectively. Calculate Digit Verification of CAS Registry Number 103438-56: (8*1)+(7*0)+(6*3)+(5*4)+(4*3)+(3*8)+(2*5)+(1*6)=98 98 % 10 = 8 So 103438-56-8 is a valid CAS Registry Number.