The CAS Registry Mumber 173437-31-5 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,7,3,4,3 and 7 respectively; the second part has 2 digits, 3 and 1 respectively. Calculate Digit Verification of CAS Registry Number 173437-31: (8*1)+(7*7)+(6*3)+(5*4)+(4*3)+(3*7)+(2*3)+(1*1)=135 135 % 10 = 5 So 173437-31-5 is a valid CAS Registry Number.