# Centered set of equations with single numbering

If I want a set of centered equations, \begin{gather} \end{gather} does the job:

\begin{gather}
i^2 = j^2 = k^2 = -1\\
ij = -ji = k
\end{gather}


If I want a set of equations with single numbering, \begin{split} \end{split} does the job:

\begin{align}
\begin{split}
i^2 = j^2 = k^2 = -1\\
ij = -ji = k
\end{split}
\end{align}


However combining the two doesn't work: I get the same result as above (non centered) if I do

\begin{gather}
\begin{split}
i^2 = j^2 = k^2 = -1\\
ij = -ji = k
\end{split}
\end{gather}


How do I fix that? Thanks in advance.

The gathered environment has been designed for this purpose.
\documentclass{article}
$$\begin{gathered} i^2 = j^2 = k^2 = -1\\ ij = -ji = k \end{gathered}$$