The CAS Registry Mumber 186603-53-2 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,8,6,6,0 and 3 respectively; the second part has 2 digits, 5 and 3 respectively. Calculate Digit Verification of CAS Registry Number 186603-53: (8*1)+(7*8)+(6*6)+(5*6)+(4*0)+(3*3)+(2*5)+(1*3)=152 152 % 10 = 2 So 186603-53-2 is a valid CAS Registry Number.