The CAS Registry Mumber 186504-88-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,8,6,5,0 and 4 respectively; the second part has 2 digits, 8 and 8 respectively. Calculate Digit Verification of CAS Registry Number 186504-88: (8*1)+(7*8)+(6*6)+(5*5)+(4*0)+(3*4)+(2*8)+(1*8)=161 161 % 10 = 1 So 186504-88-1 is a valid CAS Registry Number.