The CAS Registry Mumber 15990-73-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 1,5,9,9 and 0 respectively; the second part has 2 digits, 7 and 3 respectively. Calculate Digit Verification of CAS Registry Number 15990-73: (7*1)+(6*5)+(5*9)+(4*9)+(3*0)+(2*7)+(1*3)=135 135 % 10 = 5 So 15990-73-5 is a valid CAS Registry Number.