The CAS Registry Mumber 31843-61-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 3,1,8,4 and 3 respectively; the second part has 2 digits, 6 and 1 respectively. Calculate Digit Verification of CAS Registry Number 31843-61: (7*3)+(6*1)+(5*8)+(4*4)+(3*3)+(2*6)+(1*1)=105 105 % 10 = 5 So 31843-61-5 is a valid CAS Registry Number.