The CAS Registry Mumber 5565-37-7 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 5,5,6 and 5 respectively; the second part has 2 digits, 3 and 7 respectively. Calculate Digit Verification of CAS Registry Number 5565-37: (6*5)+(5*5)+(4*6)+(3*5)+(2*3)+(1*7)=107 107 % 10 = 7 So 5565-37-7 is a valid CAS Registry Number.