The CAS Registry Mumber 754-56-3 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 7,5 and 4 respectively; the second part has 2 digits, 5 and 6 respectively. Calculate Digit Verification of CAS Registry Number 754-56: (5*7)+(4*5)+(3*4)+(2*5)+(1*6)=83 83 % 10 = 3 So 754-56-3 is a valid CAS Registry Number.