> with (numtheory);
--------------------------------------------------------------------------------
> fft_param:=proc(n)
> pms:=max(op(invphi(n)));
> d:=gcd(pms,2*3*5);
> for i from pms while i<2*pms by d do
> if phi(i)<=n then
>   pms:=i;
> #  print(phi(pms),pms,ifactor(pms));
> fi;
> od;
> RETURN(n,phi(pms),pms,ifactor(pms),n/2*pms);
> end;
--------------------------------------------------------------------------------
> for k from 8 to 20 do fft_param(2^k); od;

                                               2
                    256, 240, 1050, (2) (3) (5)  (7), 134400

                  512, 480, 2310, (2) (3) (5) (7) (11), 591360

                                     2
                 1024, 960, 4620, (2)  (3) (5) (7) (11), 2365440

                                     3
                2048, 1920, 9240, (2)  (3) (5) (7) (11), 9461760

                                                 2
               4096, 4032, 19110, (2) (3) (5) (7)  (13), 39137280

             8192, 7680, 39270, (2) (3) (5) (7) (11) (17), 160849920

            16384, 16128, 79170, (2) (3) (5) (7) (13) (29), 648560640

                                       2
          32768, 31680, 159390, (2) (3)  (5) (7) (11) (23), 2611445760

                                                    2
          65536, 63360, 330330, (2) (3) (5) (7) (11)  (13), 10824253440

       131072, 126720, 690690, (2) (3) (5) (7) (11) (13) (23), 45265059840

                                 2
     262144, 253440, 1381380, (2)  (3) (5) (7) (11) (13) (23), 181060239360

                                         2
     524288, 518400, 2852850, (2) (3) (5)  (7) (11) (13) (19), 747857510400

                                 2        2
   1048576, 1036800, 5705700, (2)  (3) (5)  (7) (11) (13) (19), 2991430041600
--------------------------------------------------------------------------------
>