The CAS Registry Mumber 87645-56-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,7,6,4 and 5 respectively; the second part has 2 digits, 5 and 6 respectively. Calculate Digit Verification of CAS Registry Number 87645-56: (7*8)+(6*7)+(5*6)+(4*4)+(3*5)+(2*5)+(1*6)=175 175 % 10 = 5 So 87645-56-5 is a valid CAS Registry Number.