The CAS Registry Mumber 100645-89-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,0,0,6,4 and 5 respectively; the second part has 2 digits, 8 and 9 respectively. Calculate Digit Verification of CAS Registry Number 100645-89: (8*1)+(7*0)+(6*0)+(5*6)+(4*4)+(3*5)+(2*8)+(1*9)=94 94 % 10 = 4 So 100645-89-4 is a valid CAS Registry Number.