The CAS Registry Mumber 1187-21-9 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,1,8 and 7 respectively; the second part has 2 digits, 2 and 1 respectively. Calculate Digit Verification of CAS Registry Number 1187-21: (6*1)+(5*1)+(4*8)+(3*7)+(2*2)+(1*1)=69 69 % 10 = 9 So 1187-21-9 is a valid CAS Registry Number.