The CAS Registry Mumber 337909-72-5 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 3,3,7,9,0 and 9 respectively; the second part has 2 digits, 7 and 2 respectively. Calculate Digit Verification of CAS Registry Number 337909-72: (8*3)+(7*3)+(6*7)+(5*9)+(4*0)+(3*9)+(2*7)+(1*2)=175 175 % 10 = 5 So 337909-72-5 is a valid CAS Registry Number.