The CAS Registry Mumber 345309-73-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 3,4,5,3,0 and 9 respectively; the second part has 2 digits, 7 and 3 respectively. Calculate Digit Verification of CAS Registry Number 345309-73: (8*3)+(7*4)+(6*5)+(5*3)+(4*0)+(3*9)+(2*7)+(1*3)=141 141 % 10 = 1 So 345309-73-1 is a valid CAS Registry Number.