The CAS Registry Mumber 66201-87-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 6,6,2,0 and 1 respectively; the second part has 2 digits, 8 and 7 respectively. Calculate Digit Verification of CAS Registry Number 66201-87: (7*6)+(6*6)+(5*2)+(4*0)+(3*1)+(2*8)+(1*7)=114 114 % 10 = 4 So 66201-87-4 is a valid CAS Registry Number.