The CAS Registry Mumber 55609-45-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 5,5,6,0 and 9 respectively; the second part has 2 digits, 4 and 5 respectively. Calculate Digit Verification of CAS Registry Number 55609-45: (7*5)+(6*5)+(5*6)+(4*0)+(3*9)+(2*4)+(1*5)=135 135 % 10 = 5 So 55609-45-5 is a valid CAS Registry Number.