The CAS Registry Mumber 26117-42-0 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,6,1,1 and 7 respectively; the second part has 2 digits, 4 and 2 respectively. Calculate Digit Verification of CAS Registry Number 26117-42: (7*2)+(6*6)+(5*1)+(4*1)+(3*7)+(2*4)+(1*2)=90 90 % 10 = 0 So 26117-42-0 is a valid CAS Registry Number.