\newtheorem with blank printed output?

Question

Is there something I can write instead of Printed output, in \newtheorem{prg}{Printed output}[Theorem], to ensure a blank output, so that only the counted number is left after writing \begin{prg} \end{prg}?

Answer 1

Define your own theorem style (see here for the standard parameters).

\documentclass{article}
\usepackage{amsthm}
\newtheoremstyle{blank}
  {\topsep}   % ABOVESPACE
  {\topsep}   % BELOWSPACE
  {\itshape}  % BODYFONT
  {0pt}       % INDENT (empty value is the same as 0pt)
  {\bfseries} % HEADFONT
  {.}         % HEADPUNCT
  {5pt plus 1pt minus 1pt} % HEADSPACE
  {\thmnumber{#2}\thmnote{ (#3)}}       % CUSTOM-HEAD-SPEC
\newtheorem{theorem}{Theorem}
\theoremstyle{blank}
\newtheorem{prg}{}[theorem]
\begin{document}
\begin{theorem}
This is a theorem.
\end{theorem}
\begin{prg}
This has just the number.
\end{prg}
\begin{prg}[Foo]
This has the number and the annotation.
\end{prg}
\begin{theorem}
This is another theorem.
\end{theorem}
\begin{prg}
This has just the number.
\end{prg}
\begin{prg}[Foo]
This has the number and the annotation.
\end{prg}
\end{document}