The CAS Registry Mumber 186504-91-6 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, 9 and 1 respectively. Calculate Digit Verification of CAS Registry Number 186504-91: (8*1)+(7*8)+(6*6)+(5*5)+(4*0)+(3*4)+(2*9)+(1*1)=156 156 % 10 = 6 So 186504-91-6 is a valid CAS Registry Number.