# How can I multiply two numbers?

I use pgffor package and I have

\foreach \n in {1,...,10}{**something I want**}


How can I print n*(n+1) for each n?

When I write just \n*(\n+1) instead of **something I want**,

1(1+1)2(2+1)3(3+1)...


appears.

\documentclass{article}
\usepackage{pgffor}
\begin{document}
\foreach \x in {1,...,10}{%
\texttt{Something you want : \the\numexpr\x*(\x+1)/2\relax}\par}
\end{document}


Please post compilable or at least copy/pastable code so that we can see what you want to do. Until then

\documentclass{article}
\usepackage{pgffor}
\begin{document}
\foreach \x[evaluate=\x as \evalx using int(\x*(\x+1)/2)] in {1,...,10}{
\texttt{Something you want : \evalx}

}
\end{document}


Since PGF and PGFPlots are getting married to Lua as well, here is another example in LuaLaTeX.

\documentclass{article}
\begin{document}
\directlua{
for n = 1,10 do
tex.sprint(n*(n+1)/2 ..', ')
end
}
\end{document}


A more flexible solution with fp just for fun. My example below uses an extreme case which is f(x)=sin(x*π/10) instead of your simple case which is f(x)=x*(x+1)/2.

\documentclass[preview,border=12pt,12pt,varwidth]{standalone}
\usepackage{pgffor}
\usepackage[nomessages]{fp}

%\def\f[#1]{#1*(#1+1)/2}% f:x --> x*(x+1)/2
\def\f[#1]{sin(#1*pi/10)}% XTreme case just for generalization

\begin{document}
\foreach \i in {0,...,10}{%
\FPset\x{\i}%
\FPeval\y{\f[x]}%
\FPeval\y{round(y:3)}% you can use 0 to get an integer
$f(\i) = \y$ \par
}
\end{document}


## Edit

\documentclass[preview,border=12pt,12pt,varwidth]{standalone}
\usepackage{pgffor}
\usepackage[nomessages]{fp}

\def\f[#1]{#1*(#1+1)/2}% f:x --> x*(x+1)/2
%\def\f[#1]{sin(#1*pi/10)}%

\begin{document}
\foreach \i in {1,...,10}{%
\FPset\x{\i}%
\FPeval\y{\f[x]}%
\FPeval\y{round(y:0)}%
$f(\i) = \y$ \par
}
\end{document}


For comparison, here is an example using the TeX primitive integer arithmetic operators and the plain TeX \loop macro.

\documentclass{article}
\newcount\n\newcount\tn
\def\triangles#1{1%
\n=1
\loop\ifnum\n<#1