The CAS Registry Mumber 21750-58-3 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 2,1,7,5 and 0 respectively; the second part has 2 digits, 5 and 8 respectively. Calculate Digit Verification of CAS Registry Number 21750-58: (7*2)+(6*1)+(5*7)+(4*5)+(3*0)+(2*5)+(1*8)=93 93 % 10 = 3 So 21750-58-3 is a valid CAS Registry Number.