The CAS Registry Mumber 56180-65-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 5,6,1,8 and 0 respectively; the second part has 2 digits, 6 and 5 respectively. Calculate Digit Verification of CAS Registry Number 56180-65: (7*5)+(6*6)+(5*1)+(4*8)+(3*0)+(2*6)+(1*5)=125 125 % 10 = 5 So 56180-65-5 is a valid CAS Registry Number.