The CAS Registry Mumber 3103-37-5 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 3,1,0 and 3 respectively; the second part has 2 digits, 3 and 7 respectively. Calculate Digit Verification of CAS Registry Number 3103-37: (6*3)+(5*1)+(4*0)+(3*3)+(2*3)+(1*7)=45 45 % 10 = 5 So 3103-37-5 is a valid CAS Registry Number.