The CAS Registry Mumber 107553-45-7 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,7,5,5 and 3 respectively; the second part has 2 digits, 4 and 5 respectively. Calculate Digit Verification of CAS Registry Number 107553-45: (8*1)+(7*0)+(6*7)+(5*5)+(4*5)+(3*3)+(2*4)+(1*5)=117 117 % 10 = 7 So 107553-45-7 is a valid CAS Registry Number.