The CAS Registry Mumber 4361-87-9 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 4,3,6 and 1 respectively; the second part has 2 digits, 8 and 7 respectively. Calculate Digit Verification of CAS Registry Number 4361-87: (6*4)+(5*3)+(4*6)+(3*1)+(2*8)+(1*7)=89 89 % 10 = 9 So 4361-87-9 is a valid CAS Registry Number.