The CAS Registry Mumber 100644-77-7 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 4 respectively; the second part has 2 digits, 7 and 7 respectively. Calculate Digit Verification of CAS Registry Number 100644-77: (8*1)+(7*0)+(6*0)+(5*6)+(4*4)+(3*4)+(2*7)+(1*7)=87 87 % 10 = 7 So 100644-77-7 is a valid CAS Registry Number.