The CAS Registry Mumber 41977-23-5 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 4,1,9,7 and 7 respectively; the second part has 2 digits, 2 and 3 respectively. Calculate Digit Verification of CAS Registry Number 41977-23: (7*4)+(6*1)+(5*9)+(4*7)+(3*7)+(2*2)+(1*3)=135 135 % 10 = 5 So 41977-23-5 is a valid CAS Registry Number.