The CAS Registry Mumber 2516-80-5 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 2,5,1 and 6 respectively; the second part has 2 digits, 8 and 0 respectively. Calculate Digit Verification of CAS Registry Number 2516-80: (6*2)+(5*5)+(4*1)+(3*6)+(2*8)+(1*0)=75 75 % 10 = 5 So 2516-80-5 is a valid CAS Registry Number.