PrimeNth=lambda  Known, Known1  (n as long) -> {
      if n<1 then Error "Only >=1"
      if exist(known, n) then =eval(known) : exit
      if n>5 then {
           i=len(known1)
           x=eval(known1, i-1)+2
      } else  x=5 : i=2
      {
            if i=n then  =known(n) : exit
            if  frac(x) then 999
            if frac(x/2) else 999
            if frac(x/3) else 999
            x1=sqrt(x) : d=5@
            {if frac(x/d ) else 999
                  d += 2: if d>x1 then  1000
                  if frac(x/d) else 999
                  d += 4: if d<= x1 else 1000
                  loop
             }
 999     x++ : Restart
1000     i++:Append Known, i:=x  : if not exist(Known1, x) then Append Known1, x
         x++ : Loop }
}