Multiple underbrackets for sequence

Question

I wonder how to display the following sequence.

What I tried: (I am not to concered about about the type of brackets (curly, round, ...) but I would really like to have all of them in my equation...)

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\[
  1
  \underbrace{
    \underbrace{,}_{6} 
    7
    \underbrace{,}_{10}
  }_{4}
  17
  \underbrace{
    \underbrace{,}_{14}
    31
    \underbrace{,}_{18}
  }_{4}
  49
\]
\end{document}

Answer 1

\documentclass{article}

\newcommand\ubf{\kern-2\tabcolsep\upbracefill\kern-2\tabcolsep}
\begin{document}

\[
  \begin{tabular}{ccccccccccccc}
    1&&7&&17&&31&&49\\[-3pt]
     & \ubf&&\ubf&&\ubf&&\ubf\\
     & 6&&10&&14&&18\\[-3pt]
     &  &\ubf&&\ubf&&\ubf\\
     &  &4&&4&&4
  \end{tabular}
\]
\end{document}