The CAS Registry Mumber 161957-79-5 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,6,1,9,5 and 7 respectively; the second part has 2 digits, 7 and 9 respectively. Calculate Digit Verification of CAS Registry Number 161957-79: (8*1)+(7*6)+(6*1)+(5*9)+(4*5)+(3*7)+(2*7)+(1*9)=165 165 % 10 = 5 So 161957-79-5 is a valid CAS Registry Number.