The CAS Registry Mumber 426-34-6 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 4,2 and 6 respectively; the second part has 2 digits, 3 and 4 respectively. Calculate Digit Verification of CAS Registry Number 426-34: (5*4)+(4*2)+(3*6)+(2*3)+(1*4)=56 56 % 10 = 6 So 426-34-6 is a valid CAS Registry Number.