The CAS Registry Mumber 78666-41-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,8,6,6 and 6 respectively; the second part has 2 digits, 4 and 1 respectively. Calculate Digit Verification of CAS Registry Number 78666-41: (7*7)+(6*8)+(5*6)+(4*6)+(3*6)+(2*4)+(1*1)=178 178 % 10 = 8 So 78666-41-8 is a valid CAS Registry Number.