The CAS Registry Mumber 338730-21-5 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 3,3,8,7,3 and 0 respectively; the second part has 2 digits, 2 and 1 respectively. Calculate Digit Verification of CAS Registry Number 338730-21: (8*3)+(7*3)+(6*8)+(5*7)+(4*3)+(3*0)+(2*2)+(1*1)=145 145 % 10 = 5 So 338730-21-5 is a valid CAS Registry Number.