The CAS Registry Mumber 206554-13-4 includes 9 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 6 digits, 2,0,6,5,5 and 4 respectively; the second part has 2 digits, 1 and 3 respectively. Calculate Digit Verification of CAS Registry Number 206554-13: (8*2)+(7*0)+(6*6)+(5*5)+(4*5)+(3*4)+(2*1)+(1*3)=114 114 % 10 = 4 So 206554-13-4 is a valid CAS Registry Number.