The CAS Registry Mumber 24037-21-6 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,4,0,3 and 7 respectively; the second part has 2 digits, 2 and 1 respectively. Calculate Digit Verification of CAS Registry Number 24037-21: (7*2)+(6*4)+(5*0)+(4*3)+(3*7)+(2*2)+(1*1)=76 76 % 10 = 6 So 24037-21-6 is a valid CAS Registry Number.