The CAS Registry Mumber 5881-42-5 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 5,8,8 and 1 respectively; the second part has 2 digits, 4 and 2 respectively. Calculate Digit Verification of CAS Registry Number 5881-42: (6*5)+(5*8)+(4*8)+(3*1)+(2*4)+(1*2)=115 115 % 10 = 5 So 5881-42-5 is a valid CAS Registry Number.