The CAS Registry Mumber 97643-27-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 9,7,6,4 and 3 respectively; the second part has 2 digits, 2 and 7 respectively. Calculate Digit Verification of CAS Registry Number 97643-27: (7*9)+(6*7)+(5*6)+(4*4)+(3*3)+(2*2)+(1*7)=171 171 % 10 = 1 So 97643-27-1 is a valid CAS Registry Number.