The CAS Registry Mumber 100517-15-5 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,0,5,1 and 7 respectively; the second part has 2 digits, 1 and 5 respectively. Calculate Digit Verification of CAS Registry Number 100517-15: (8*1)+(7*0)+(6*0)+(5*5)+(4*1)+(3*7)+(2*1)+(1*5)=65 65 % 10 = 5 So 100517-15-5 is a valid CAS Registry Number.