{def sweeney
 {def sweeney.set!
  {lambda {:s :r :k :i}
   {A.set! :i {+ {A.get :i :s} {/ :r :k}} :s}
 }}
 {def sweeney.loop
  {lambda {:n :s :r :k}
   {if {<= :r 1.e-10}
    then gamma = {- {A.get 1 :s} {A.get 0 :s} {log :n}} with k=:k
    else {sweeney.loop :n
                       {sweeney.set! :s {* :r {/ :n :k}} :k {% :k 2}}
                       {* :r {/ :n :k}}
                       {+ :k 1} }
 }}}
 {lambda {:n}
  {sweeney.loop :n {A.new 0 :n} :n 2} }}
-> sweeney

{sweeney 21}
-> gamma = 0.577215664563631 with k=76
          (0.57721566456363 target)