The CAS Registry Mumber 127977-31-5 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,7,9,7 and 7 respectively; the second part has 2 digits, 3 and 1 respectively. Calculate Digit Verification of CAS Registry Number 127977-31: (8*1)+(7*2)+(6*7)+(5*9)+(4*7)+(3*7)+(2*3)+(1*1)=165 165 % 10 = 5 So 127977-31-5 is a valid CAS Registry Number.