The CAS Registry Mumber 86921-56-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 8,6,9,2 and 1 respectively; the second part has 2 digits, 5 and 6 respectively. Calculate Digit Verification of CAS Registry Number 86921-56: (7*8)+(6*6)+(5*9)+(4*2)+(3*1)+(2*5)+(1*6)=164 164 % 10 = 4 So 86921-56-4 is a valid CAS Registry Number.