The CAS Registry Mumber 134755-13-8 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,3,4,7,5 and 5 respectively; the second part has 2 digits, 1 and 3 respectively. Calculate Digit Verification of CAS Registry Number 134755-13: (8*1)+(7*3)+(6*4)+(5*7)+(4*5)+(3*5)+(2*1)+(1*3)=128 128 % 10 = 8 So 134755-13-8 is a valid CAS Registry Number.