The CAS Registry Mumber 188616-78-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,8,8,6,1 and 6 respectively; the second part has 2 digits, 7 and 8 respectively. Calculate Digit Verification of CAS Registry Number 188616-78: (8*1)+(7*8)+(6*8)+(5*6)+(4*1)+(3*6)+(2*7)+(1*8)=186 186 % 10 = 6 So 188616-78-6 is a valid CAS Registry Number.