The CAS Registry Mumber 7107-53-1 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 7,1,0 and 7 respectively; the second part has 2 digits, 5 and 3 respectively. Calculate Digit Verification of CAS Registry Number 7107-53: (6*7)+(5*1)+(4*0)+(3*7)+(2*5)+(1*3)=81 81 % 10 = 1 So 7107-53-1 is a valid CAS Registry Number.