The CAS Registry Mumber 2441-81-8 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 2,4,4 and 1 respectively; the second part has 2 digits, 8 and 1 respectively. Calculate Digit Verification of CAS Registry Number 2441-81: (6*2)+(5*4)+(4*4)+(3*1)+(2*8)+(1*1)=68 68 % 10 = 8 So 2441-81-8 is a valid CAS Registry Number.