The CAS Registry Mumber 173099-58-6 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,7,3,0,9 and 9 respectively; the second part has 2 digits, 5 and 8 respectively. Calculate Digit Verification of CAS Registry Number 173099-58: (8*1)+(7*7)+(6*3)+(5*0)+(4*9)+(3*9)+(2*5)+(1*8)=156 156 % 10 = 6 So 173099-58-6 is a valid CAS Registry Number.