The CAS Registry Mumber 134720-42-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,4,7,2 and 0 respectively; the second part has 2 digits, 4 and 2 respectively. Calculate Digit Verification of CAS Registry Number 134720-42: (8*1)+(7*3)+(6*4)+(5*7)+(4*2)+(3*0)+(2*4)+(1*2)=106 106 % 10 = 6 So 134720-42-6 is a valid CAS Registry Number.