Here is a list of the mathematical symbols that can be represented with ASCII letters.

Dec	Hex	Unicode	HTML-char	Char	Description
8722	2212	U+2212		−	Minus Sign
43	2B	U+002b		+	Plus Sign
177	B1	U+00b1	±	±	Plus or Minus Sign
215	D7	U+00d7	×	×	Multiplication Sign
247	F7	U+00f7	÷	÷	Division Sign
37	25	U+0025		%	Percent Sign
8240	2030	U+2030		‰	Per Million Sign
61	3D	U+003d		=	Equal Sign
8800	2260	U+2260		≠	Not Equal To Sign
8776	2248	U+2248		≈	Approximately Equal Sign
8801	2261	U+2261		≡	Identical To Sign
60	3C	U+003c	&lt;	<	Less Than Sign
62	3E	U+003e	&gt;	>	Greater Than Sign
8804	2264	U+2264		≤	Less Than or Equal To Sign
8805	2265	U+2265		≥	Greater Than or Equal To Sign
8734	221E	U+221e		∞	Infinity Sign
8539	215B	U+215b		⅛	One Eighth Fraction
188	BC	U+00bc	&#188;	¼	One Quarter Fraction
8540	215C	U+215c		⅜	Three Eighths Fraction
189	BD	U+00bd	&#189;	½	One Half Fraction
8541	215D	U+215d		⅝	Five Eighths Fraction
190	BE	U+00be	&#190;	¾	Three Quarters Fraction
8542	215E	U+215e		⅞	Seven Eighths Fraction
8747	222B	U+222b		∫	Integral Sign
8706	2202	U+2202		∂	Partial Differential Sign
8710	2206	U+2206		∆	Increment Sign
8719	220F	U+220f		∏	N-ary Product Sign
8721	2211	U+2211		∑	N-ary Sum Sign
8730	221A	U+221a		√	Square Root Sign
8735	221F	U+221f		∟	Right Angle Sign
8745	2229	U+2229		∩	Intersection Sign
8729	2219	U+2219		∙	Bullet Operator
402	192	U+0192		ƒ	Function Sign
8260	2044	U+2044		⁄	Fraction Slash
8896	22C0	U+22c0		⋀	And
8744	2228	U+2228		∨	Or
206	CE	U+00ce	&#206;	Î	is an element of
8594	2192	U+2192		→	implies
8596	2194	U+2194		↔	if and only if
8704	2200	U+2200		∀	for all
8707	2203	U+2203		∃	there exits

The HTML characters that aren't written out works like this, add a '&' and '%' before the decimal value and a ';' behind it and you can output it as the character, like this:

ƒ = ƒ

or

‰ = ‰

As simple as that