The CAS Registry Mumber 159635-23-1 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 1,5,9,6,3 and 5 respectively; the second part has 2 digits, 2 and 3 respectively. Calculate Digit Verification of CAS Registry Number 159635-23: (8*1)+(7*5)+(6*9)+(5*6)+(4*3)+(3*5)+(2*2)+(1*3)=161 161 % 10 = 1 So 159635-23-1 is a valid CAS Registry Number.