fftw and online DFT calculator get different results

fftw and online DFT calculator get different results

I calculated the FFT of array {1,2,3,4,5,6} with fftw/C++ and an online
calculator
(http://calculator-fx.com/calculator/fast-fourier-transform-calculator-fft/1d-discrete-fourier-transform).
And the results seemed to be a bit different.
fftw output:
0 21.000000 0.000000
1 -3.000000 5.196152
2 -3.000000 1.732051
3 -3.000000 0.000000
4 0.000000 0.000000
5 0.000000 0.000000
Online calculator output:
21 + 0j
-3 + 5.196152j
-3 + 1.732051j
-3 + 0j
-3 - 1.732051j
-3 - 5.196152j
As is shown above, the latter two results of fftw turned to be zero. Can't
figure out why. Could anybody help me out? Thanks.
[EDITED] cpp code:
int main()
{
fftw_complex *out;
fftw_plan plan;
double arr[]={1,2,3,4,5,6};
int n = sizeof(arr)/sizeof(double);
out = (fftw_complex*)fftw_malloc ( sizeof ( fftw_complex ) * n );
plan = fftw_plan_dft_r2c_1d ( n, arr, out, FFTW_ESTIMATE );
fftw_execute ( plan );
for (int i = 0; i < n; i++ )
{
printf ( " %3d %12lf %12lf\n", i, out[i][0], out[i][1] );
}
fftw_free(out);
fftw_destroy_plan(plan);
return 0;
}