The CAS Registry Mumber 19856-66-7 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,9,8,5 and 6 respectively; the second part has 2 digits, 6 and 6 respectively. Calculate Digit Verification of CAS Registry Number 19856-66: (7*1)+(6*9)+(5*8)+(4*5)+(3*6)+(2*6)+(1*6)=157 157 % 10 = 7 So 19856-66-7 is a valid CAS Registry Number.