The CAS Registry Mumber 31883-87-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 3,1,8,8 and 3 respectively; the second part has 2 digits, 8 and 7 respectively. Calculate Digit Verification of CAS Registry Number 31883-87: (7*3)+(6*1)+(5*8)+(4*8)+(3*3)+(2*8)+(1*7)=131 131 % 10 = 1 So 31883-87-1 is a valid CAS Registry Number.