The CAS Registry Mumber 2201-34-5 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 2,2,0 and 1 respectively; the second part has 2 digits, 3 and 4 respectively. Calculate Digit Verification of CAS Registry Number 2201-34: (6*2)+(5*2)+(4*0)+(3*1)+(2*3)+(1*4)=35 35 % 10 = 5 So 2201-34-5 is a valid CAS Registry Number.