The CAS Registry Mumber 91522-56-4 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,1,5,2 and 2 respectively; the second part has 2 digits, 5 and 6 respectively. Calculate Digit Verification of CAS Registry Number 91522-56: (7*9)+(6*1)+(5*5)+(4*2)+(3*2)+(2*5)+(1*6)=124 124 % 10 = 4 So 91522-56-4 is a valid CAS Registry Number.