The CAS Registry Mumber 55609-39-7 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 5,5,6,0 and 9 respectively; the second part has 2 digits, 3 and 9 respectively. Calculate Digit Verification of CAS Registry Number 55609-39: (7*5)+(6*5)+(5*6)+(4*0)+(3*9)+(2*3)+(1*9)=137 137 % 10 = 7 So 55609-39-7 is a valid CAS Registry Number.