The CAS Registry Mumber 109-34-2 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 1,0 and 9 respectively; the second part has 2 digits, 3 and 4 respectively. Calculate Digit Verification of CAS Registry Number 109-34: (5*1)+(4*0)+(3*9)+(2*3)+(1*4)=42 42 % 10 = 2 So 109-34-2 is a valid CAS Registry Number.