HTML doesn't do equations but it does include some special symbols that you can use to draw simple equations, logical expressions, and other interesting results. This page lists the codes for generating some useful special symbols.

Operations
Name	Symbol	Code
For all	∀	∀
Exists	∃	∃
Not	¬	¬
And	∧	∧
Or	∨	∨
Intersection	∩	∩
Union	∪	∪
Plus/minus	±	±
Minus/plus	∓	∓
Times	×	×
Partial derivative	∂	∂
Solid dot	∙	∙
Middle dot	·	·
Circle times	⊗	⊗
Circle plus	⊕	⊕
Division	÷	÷
Product	∏	∏
Sum	∑	∑
Square root	√	√
Integral	∫	∫
Relations
Contains	∍	∍
Is contained by	∈	∈
Is not contained by	∉	∉
Less than	<	&lt;
Less than or equal to	≤	&le;
Greater than	>	&gt;
Greater than or equal to	≥	&ge;
Congruent	≅	&cong;
Perpendicular	⊥	&perp;
Vertical bar	|	&#124;
Broken vertical bar (pipe)	¦	&brvbar;
Not equal to	≠	&ne;
Equivalent to	≡	&equiv;
Approximately equal to	≈	&asymp;
Similar to	∼	&sim;
Empty set	∅	&empty;
Contains properly	⊃	&sup;
Contains	⊇	&supe;
Not contained in	⊄	&nsub;
Proper subset of	&sub	&sub;
Subset of	&sube	&sube;
Arrows and Brackets
Double arrow	↔	&harr;
Left arrow	←	&larr;
Right arrow	→	&rarr;
Up arrow	↑	&uarr;
Down arrow	↓	&darr;
Double arrow	⇔	&hArr;
Double left arrow	⇐	&lArr;
Double right arrow	⇒	&rArr;
Double up arrow	⇑	&uArr;
Double down arrow	⇓	&dArr;
Double arrow	⇔	&hArr;
Ellipsis	…	&hellip;
Left angle quote	‹	&lsaquo;
Left double angle quote	«	&laquo;
Right angle quote	›	&rsaquo;
Right double angle quote	»	&raquo;
Lowercase Greek
Alpha	α	&alpha;
Beta	β	&beta;
Gamma	γ	&gamma;
Delta	δ	&delta;
Epsilon	ε	&epsilon;
Zeta	ζ	&zeta;
Eta	η	&eta;
Theta	θ	&theta;
Iota	ι	&iota;
Kappa	κ	&kappa;
Lambda	λ	&lambda;
Mu	μ	&mu;
Nu	ν	&nu;
Xi	ξ	&xi;
Omicron	ο	&omicron;
Pi	π	&pi;
Rho	ρ	&rho;
Sigma	σ	&sigma;
Tau	τ	&tau;
Upsilon	υ	&upsilon;
Phi	φ	&phi;
Chi	χ	&chi;
Psi	ψ	&psi;
Omega	ω	&omega;
Uppercase Greek
Alpha	Α	&Alpha;
Beta	Β	&Beta;
Gamma	Γ	&Gamma;
Delta	Δ	&Delta;
Epsilon	Ε	&Epsilon;
Zeta	Ζ	&Zeta;
Eta	Η	&Eta;
Theta	Θ	&Theta;
Iota	Ι	&Iota;
Kappa	Κ	&Kappa;
Lambda	Λ	&Lambda;
Mu	Μ	&Mu;
Nu	Ν	&Nu;
Xi	Ξ	&Xi;
Omicron	Ο	&Omicron;
Pi	Π	&Pi;
Rho	Ρ	&Rho;
Sigma	Σ	&Sigma;
Tau	Τ	&Tau;
Upsilon	Υ	&Upsilon;
Phi	Φ	&Phi;
Chi	Χ	&Chi;
Psi	Ψ	&Psi;
Omega	Ω	&Omega;
Editing
Pilcrow (paragraph)	¶	&para;
Section	§	&sect;
Dagger	†	&dagger;
Double dagger	‡	&Dagger;
Superscript 1	¹	&sup1;
Superscript 2	²	&sup2;
Superscript 3	³	&sup3;
Superscript n	ⁿ	&#8319;
Fractions
One half	½	&frac12;
One quarter	¼	&frac14;
Three quarters	¾	&frac34;
Fraction slash	⁄	&frasl;
Example fraction	4⁄5	<sup>4</sup>&frasl;<sub>5</sub>
Currency
Currency	¤	&curren;
Cent	¢	&cent;
Pound	£	&pound;
Euro	€	&euro;
Yen	¥	&yen;
Miscellaneous
Non-breaking space		&nbsp;
Ampersand	&	&amp;
Prime	′	&prime;
Double prime	″	&Prime;
Quote	"	&quot;
Therefore	∴	&there4;
Infinity	∞	&infin;
Degree	°	&deg;
Aleph	ℵ	&alefsym;
Nabla	∇	&nabla;
Registration mark	®	&reg;
Copyright	©	&copy;
Trademark	™	&trade;
Spades	♠	&spades;
Hearts	♥	&hearts;
Clubs	♣	&clubs;
Diamonds	♦	&diams;
Tilde	˜	&tilde;
Bottom quote	‚	&sbquo;
Bottom double quote	„	&#132;
Left quote	‘	&lsquo;
Left double quote	“	&ldquo;
Right quote	’	&rsquo;
Right double quote	”	&rdquo;
Small bullet	•	&#149;
En dash	–	&ndash;
Em dash	—	&mdash;
Micro	µ	&micro;
Inverted question mark	¿	&iquest;
Inverted exclamation point	¡	&iexcl;
Care of	℅	&#8453;
Horizontal bar	―	&#8213;
Triangle bullet	‣	&#8227;
Overline	‾	&oline;
Double exclamation point	‼	&#8252;
Number word	№	&#8470;
Female	♀	&#9792;
Male	♂	&#9794;
Quarter note	♩	&#9833;
Eighth note	♪	&#9834;
Double eighth note	♬	&#9836;
Flat	♭	&#9837;
Sharp	♯	&#9839;
Horizontal tab	A B	&#09;
Female ordinal indicator	ª	&ordf;
Male ordinal indicator	º	&ordm;
Unknown		&#129;
Function	ƒ	&#131;
Permille	‰	&permil;
Hatchek	ˆ	&#136;
Acute accent	´	&#180;
Cedilla	¸	&cedil;
Thorn	þ	&thorn;
Thorn	Þ	&THORN;

The most recent versions of most major browsers should be able to display these symbols if they are configured correctly. For example, they work on my system in Firefox 3.6.3.

If Internet Explorer is giving you problems, see Displaying Special Characters or search the web for solutions.