The CAS Registry Mumber 16541-52-9 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,6,5,4 and 1 respectively; the second part has 2 digits, 5 and 2 respectively. Calculate Digit Verification of CAS Registry Number 16541-52: (7*1)+(6*6)+(5*5)+(4*4)+(3*1)+(2*5)+(1*2)=99 99 % 10 = 9 So 16541-52-9 is a valid CAS Registry Number.