The CAS Registry Mumber 5821-78-3 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 5,8,2 and 1 respectively; the second part has 2 digits, 7 and 8 respectively. Calculate Digit Verification of CAS Registry Number 5821-78: (6*5)+(5*8)+(4*2)+(3*1)+(2*7)+(1*8)=103 103 % 10 = 3 So 5821-78-3 is a valid CAS Registry Number.