If you are using the security restrictions, you may want to use a good list of allowed commands. Here is a big list of undangerous commands. You can copy&paste it on the input filter settings page.

\text \textit \textbf \textrm \texttt \textsf \emph \hbox \mbox \frac \cfrac \over \binom \choose \atop \left \right \big \Big \bigg \Bigg \bigl \Bigl \biggl \Biggl \bigr \Bigr \biggr \Biggr \mathop \mathrel \mathord \mathbin \mathopen \mathclose \mathpunct \mathinner \limits \nolimits \displaylimits \quad \qquad \hat \widehat \dot \ddot \bar \overline \underline \overbrace \underbrace \overleftarrow \overrightarrow \overleftrightarrow \check \acute \grave \vec \breve \tilde \widetilde \mathbf \mathbb \mathrm \mathit \mathcal \mathfrak \mathsf \mathtt \boldsymbol \rm \bf \it \cal \tt \sf \Bbb \bold \displaystyle \textstyle \scriptstyle \scriptscriptstyle \alpha \beta \gamma \delta \epsilon \varepsilon \zeta \eta \vartheta \theta \iota \kappa \varkappa \lambda \mu \nu \pi \varpi \rho \varrho \sigma \varsigma \tau \upsilon \phi \varphi \chi \psi \omega \xi \digamma \Gamma \Delta \Theta \Lambda \Pi \Sigma \Upsilon \Phi \Psi \Omega \Xi \ast \implies \neg \ne \ge \le \land \lor \gets \to \vert \lvert \rvert \Vert \lVert \rVert \lfloor \rfloor \lceil \rceil \lbrace \rbrace \langle \rangle \lbrack \rbrack \aleph \beth \gimel \daleth \wp \ell \P \imath \forall \exists \Finv \Game \partial \Re \Im \leftarrow \rightarrow \longleftarrow \longrightarrow \Leftarrow \Rightarrow \Longleftarrow \Longrightarrow \mapsto \longmapsto \leftrightarrow \Leftrightarrow \longleftrightarrow \Longleftrightarrow \uparrow \Uparrow \downarrow \Downarrow \updownarrow \Updownarrow \searrow \nearrow \swarrow \nwarrow \hookrightarrow \hookleftarrow \upharpoonright \upharpoonleft \downharpoonright \downharpoonleft \rightharpoonup \rightharpoondown \leftharpoonup \leftharpoondown \nleftarrow \nrightarrow \supset \subset \supseteq \subseteq \sqsupset \sqsubset \sqsupseteq \sqsubseteq \supsetneq \subsetneq \in \ni \notin \iff \mid \sim \simeq \approx \propto \equiv \cong \neq \ll \gg \geq \leq \triangleleft \triangleright \trianglelefteq \trianglerighteq \models \vdash \Vdash \vDash \lesssim \nless \ngeq \nleq \times \div \wedge \vee \oplus \otimes \cap \cup \sqcap \sqcup \smile \frown \smallsmile \smallfrown \setminus \smallsetminus \And \star \triangle \wr \infty \circ \hbar \lnot \nabla \prime \backslash \pm \mp \emptyset \varnothing \S \angle \colon \Diamond \nmid \square \Box \checkmark \complement \eth \hslash \mho \flat \sharp \natural \bullet \dagger \ddagger \clubsuit \spadesuit \heartsuit \diamondsuit \top \bot \perp \ldots \cdot \cdots \vdots \ddots \dots \dotsb \circledR \yen \maltese \circledS \Bbbk \jmath \ulcorner \urcorner \llcorner \lrcorner \dashrightarrow \dashleftarrow \backprime \vartriangle \blacktriangle \triangledown \blacktriangledown \blacksquare \lozenge \blacklozenge \bigstar \sphericalangle \measuredangle \dotplus \ltimes \rtimes \Cap \leftthreetimes \rightthreetimes \Cup \barwedge \curlywedge \veebar \curlyvee \doublebarwedge \boxminus \circleddash \boxtimes \circledast \boxdot \circledcirc \boxplus \centerdot \divideontimes \intercal \leqq \geqq \leqslant \geqslant \eqslantless \eqslantgtr \gtrsim \lessapprox \gtrapprox \approxeq \eqsim \lessdot \gtrdot \lll \ggg \lessgtr \gtrless \lesseqgtr \gtreqless \lesseqqgtr \gtreqqless \doteqdot \eqcirc \risingdotseq \circeq \fallingdotseq \triangleq \backsim \thicksim \backsimeq \thickapprox \subseteqq \supseteqq \Subset \Supset \preccurlyeq \succcurlyeq \curlyeqprec \curlyeqsucc \precsim \succsim \precapprox \succapprox \Vvdash \shortmid \shortparallel \bumpeq \between \Bumpeq \varpropto \backepsilon \blacktriangleleft \blacktriangleright \therefore \because \ngtr \nleqslant \ngeqslant \nleqq \ngeqq \lneqq \gneqq \lvertneqq \gvertneqq \lnsim \gnsim \lnapprox \gnapprox \nprec \nsucc \npreceq \nsucceq \precneqq \succneqq \precnsim \succnsim \precnapprox \succnapprox \nsim \ncong \nshortmid \nshortparallel \nmid \nparallel \nvdash \nvDash \nVdash \nVDash \ntriangleleft \ntriangleright \ntrianglelefteq \ntrianglerighteq \nsubseteq \nsupseteq \nsubseteqq \nsupseteqq \subsetneq \supsetneq \varsubsetneq \varsupsetneq \subsetneqq \supsetneqq \varsubsetneqq \varsupsetneqq \leftleftarrows \rightrightarrows \leftrightarrows \rightleftarrows \Lleftarrow \Rrightarrow \twoheadleftarrow \twoheadrightarrow \leftarrowtail \rightarrowtail \looparrowleft \looparrowright \leftrightharpoons \rightleftharpoons \curvearrowleft \curvearrowright \circlearrowleft \circlearrowright \Lsh \Rsh \upuparrows \downdownarrows \multimap \rightsquigarrow \leftrightsquigarrow \nLeftarrow \nRightarrow \nleftrightarrow \nLeftrightarrow \pitchfork \nexists \lhd \rhd \unlhd \unrhd \leadsto \uplus \diamond \bigtriangleup \bigtriangledown \ominus \oslash \odot \bigcirc \amalg \prec \succ \preceq \succeq \dashv \asymp \doteq \parallel \bowtie \surd \doublecap \restriction \llless \gggtr \Doteq \doublecup \dasharrow \vartriangleleft \vartriangleright \Join \sum \prod \int \iint \iiint \iiiint \oint \bigcap \bigodot \bigcup \bigotimes \coprod \bigsqcup \bigoplus  \bigvee \biguplus \bigwedge \textbackslash \textvisiblespace \textasciicircum \textasciitilde \A \B \C \D \E \F \G \H \I \J \K \L \M \N \O \P \Q \R \S \T \U \V \W \X \Y \Z \Reals \reals \Z \N \natnums \Complex \cnums \alefsym \alef \larr \rarr \Larr \lArr \Rarr \rArr \uarr \uArr \Uarr \darr \dArr \Darr \lrarr \harr \Lrarr \Harr \lrArr \hAar \sub \supe \sube \infin \lang \rang \real \image \bull \weierp \isin \plusmn \Dagger \exist \sect \clubs \spades \hearts \diamonds \sdot \ang \thetasym \Alpha \Beta \Epsilon \Zeta \Eta \Iota \Kappa \Mu \Nu \Rho \Tau \Chi \arcsec \arccsc \arccot \sgn \sqrt \sin \cos \tan \not \substack \overset \underset \log \ln