org-format-latex-header

org-format-latex-header is a variable defined in `org.el'.
Its value is

"\\documentclass{article}\n\\usepackage[usenames]{color}\n[PACKAGES]\n[DEFAULT-PACKAGES]\n\\pagestyle{empty}             % do not remove\n% The settings below are copied from fullpage.sty\n\\setlength{\\textwidth}{\\paperwidth}\n\\addtolength{\\textwidth}{-3cm}\n\\setlength{\\oddsidemargin}{1.5cm}\n\\addtolength{\\oddsidemargin}{-2.54cm}\n\\setlength{\\evensidemargin}{\\oddsidemargin}\n\\setlength{\\textheight}{\\paperheight}\n\\addtolength{\\textheight}{-\\headheight}\n\\addtolength{\\textheight}{-\\headsep}\n\\addtolength{\\textheight}{-\\footskip}\n\\addtolength{\\textheight}{-3cm}\n\\setlength{\\topmargin}{1.5cm}\n\\addtolength{\\topmargin}{-2.54cm}"

Documentation:
The document header used for processing LaTeX fragments.
It is imperative that this header make sure that no page number
appears on the page. The package defined in the variables
`org-latex-default-packages-alist' and `org-latex-packages-alist'
will either replace the placeholder "[PACKAGES]" in this
header, or they will be appended.

You can customize this variable.