The CAS Registry Mumber 80506-56-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,0,5,0 and 6 respectively; the second part has 2 digits, 5 and 6 respectively. Calculate Digit Verification of CAS Registry Number 80506-56: (7*8)+(6*0)+(5*5)+(4*0)+(3*6)+(2*5)+(1*6)=115 115 % 10 = 5 So 80506-56-5 is a valid CAS Registry Number.