The CAS Registry Mumber 73174-56-8 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 7,3,1,7 and 4 respectively; the second part has 2 digits, 5 and 6 respectively. Calculate Digit Verification of CAS Registry Number 73174-56: (7*7)+(6*3)+(5*1)+(4*7)+(3*4)+(2*5)+(1*6)=128 128 % 10 = 8 So 73174-56-8 is a valid CAS Registry Number.