how to receive a triangle shape output in Fortran

I was trying to write code with this output:

      1
    1 2 1
  1 2 3 2 1
1 2 3 4 3 2 1

This is what I did :

program pascal
implicit none
integer i,j,k,p,n
write (*, '("input n: ")', advance="no")
read(*,*) n
do i=0,n-1
   p=1
   do j=1,n-1-i
      write(*,'(3X)', advance="no")
   enddo
   do k = 0,i
      write(*,'(I6)', advance="no") p
      p = p*(i-k)/(k+1)
   enddo
   write(*, '(/)')
end do
endprogram

which the output is pascal triangle. How can I fix it?