The CAS Registry Mumber 127980-78-3 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,2,7,9,8 and 0 respectively; the second part has 2 digits, 7 and 8 respectively. Calculate Digit Verification of CAS Registry Number 127980-78: (8*1)+(7*2)+(6*7)+(5*9)+(4*8)+(3*0)+(2*7)+(1*8)=163 163 % 10 = 3 So 127980-78-3 is a valid CAS Registry Number.