How to set the number of the first citation?

Question

I am using BibTeX and natbib for my citations. In the bibliography the first entry usually starts with [1]. Now I would like to shift all the numbers in the bibliography and text by a certain offset, e.g. 15, so that the first item is called 16 in this document.

Answer 1

I'm not sure why you want to do this (there are various packages that deal with multiple/subdivided bibliographies), but you could use the etoolbox package to append natbib's definition of the thebibliography environment.

\documentclass{article}

\usepackage[numbers]{natbib}

\usepackage{etoolbox}

\makeatletter
\apptocmd{\thebibliography}{\global\c@NAT@ctr 15\relax}{}{}
\makeatother

\usepackage{filecontents}

\begin{filecontents}{\jobname.bib}
@misc{A01,
  author = {Author, A.},
  year = {2001},
  title = {Alpha},
}
@misc{B02,
  author = {Buthor, B.},
  year = {2002},
  title = {Bravo},
}
\end{filecontents}

\begin{document}

Some text \citep{A01,B02}.

\bibliographystyle{plainnat}
\bibliography{\jobname}

\end{document}