The CAS Registry Mumber 2638-74-6 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 2,6,3 and 8 respectively; the second part has 2 digits, 7 and 4 respectively. Calculate Digit Verification of CAS Registry Number 2638-74: (6*2)+(5*6)+(4*3)+(3*8)+(2*7)+(1*4)=96 96 % 10 = 6 So 2638-74-6 is a valid CAS Registry Number.