The CAS Registry Mumber 134387-71-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,4,3,8 and 7 respectively; the second part has 2 digits, 7 and 1 respectively. Calculate Digit Verification of CAS Registry Number 134387-71: (8*1)+(7*3)+(6*4)+(5*3)+(4*8)+(3*7)+(2*7)+(1*1)=136 136 % 10 = 6 So 134387-71-6 is a valid CAS Registry Number.