The CAS Registry Mumber 100856-63-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,0,8,5 and 6 respectively; the second part has 2 digits, 6 and 3 respectively. Calculate Digit Verification of CAS Registry Number 100856-63: (8*1)+(7*0)+(6*0)+(5*8)+(4*5)+(3*6)+(2*6)+(1*3)=101 101 % 10 = 1 So 100856-63-1 is a valid CAS Registry Number.