z = fact(z)/(2*pow(log(2),n+1));

if(fmod(z,1)>=0.5) z = floor(z) + 1;
else z = floor(z);


I tried the example test case and got true, but got WA with 1st test case... T_T

I sent your formula and got AC. Try to output answer so:

cout << fixed << setprecision(0) << z;

or so:

printf("%.0lf",z);

And you must use double instead of float

function g(x,k:longint):comp;
var i:longint; q:comp;
begin
    q:=1;
    for i:=1 to k do q:=q*i;
        g:=q*x;
end;
var
f:array[0..20,0..20] of longint;
a:array[0..20] of comp;
    i,j,n,k:longint;
begin
for i:=0 to 10 do begin f[i,1]:=1; f[i,i]:=1; end;
f[0,1]:=0;
for i:=1 to 10 do
    for j:=2 to i-1 do f[i,j]:=f[i-1,j-1]+f[i-1,j]*j;
for i:=2 to 10 do
    for j:=1 to 10 do a[i]:=a[i]+g(f[i,j],j);
readln(n);
    while n>0 do
        begin
        writeln(a[n]:0:0);
        readln(n);
        end;
end.