The CAS Registry Mumber 105291-54-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,5,2,9 and 1 respectively; the second part has 2 digits, 5 and 4 respectively. Calculate Digit Verification of CAS Registry Number 105291-54: (8*1)+(7*0)+(6*5)+(5*2)+(4*9)+(3*1)+(2*5)+(1*4)=101 101 % 10 = 1 So 105291-54-1 is a valid CAS Registry Number.