cre[ja_, 
        jb_]  :=  (2 ja + 1) (2  jb + 
            1) (ThreeJSymbol[{ja, -1/2}, {2, 0}, {jb, 
                1/2}])^2

cre[3/2, 1/2]

cre[5/2, 1/2]

a  =  
      1.1198 10^(18) (10.8304)^2/(7306.4)^5/5

1/a