The CAS Registry Mumber 102991-73-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,2,9,9 and 1 respectively; the second part has 2 digits, 7 and 3 respectively. Calculate Digit Verification of CAS Registry Number 102991-73: (8*1)+(7*0)+(6*2)+(5*9)+(4*9)+(3*1)+(2*7)+(1*3)=121 121 % 10 = 1 So 102991-73-1 is a valid CAS Registry Number.