The CAS Registry Mumber 6874-18-6 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 6,8,7 and 4 respectively; the second part has 2 digits, 1 and 8 respectively. Calculate Digit Verification of CAS Registry Number 6874-18: (6*6)+(5*8)+(4*7)+(3*4)+(2*1)+(1*8)=126 126 % 10 = 6 So 6874-18-6 is a valid CAS Registry Number.