The CAS Registry Mumber 75556-27-3 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,5,5,5 and 6 respectively; the second part has 2 digits, 2 and 7 respectively. Calculate Digit Verification of CAS Registry Number 75556-27: (7*7)+(6*5)+(5*5)+(4*5)+(3*6)+(2*2)+(1*7)=153 153 % 10 = 3 So 75556-27-3 is a valid CAS Registry Number.