The CAS Registry Mumber 9055-26-9 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 9,0,5 and 5 respectively; the second part has 2 digits, 2 and 6 respectively. Calculate Digit Verification of CAS Registry Number 9055-26: (6*9)+(5*0)+(4*5)+(3*5)+(2*2)+(1*6)=99 99 % 10 = 9 So 9055-26-9 is a valid CAS Registry Number.