The crawler bot for this one is looking specifically for numbers in the text content of web pages; especially floating point numbers, in a variety of formats, including scientific notation, numbers with commas (both American and foreign versions) and your "vulgar fractions." For our purposes it would probably be best to index "6.000" as -both- "six (six point 0 0 0)" and "six thousand." Now that I mention it, I guess spelled out numbers in a few major languages should be implementable without too many lines of code.
The web-facing page will take an input that represents a quantity, and will also ideally be fairly eclectic in interpreting numeric, although it is not as mission critical here, but we seem to have the pattern matching software already in place, so why not? The output should be the indexed numbers that are equal to the search term, if any, accompanied by links to the pages where they were found. These zero or more exact matches should be followed by near matches in increasing order by absolute difference (which should produce the same sort order as the square of the difference).
An additional feature could be a second (optional) input for a function of one real value that returns a real result. In this case the search result on search term x would give pages containing numbers y such that x≊f(y) (or perhaps as an added option, f(x)≊f(y)). This part of the system would probably interface with some Maxima-type program to solve for "multiple inverses."-- LoriZ, Jul 22 2013 This could be quite useful ...-- 8th of 7, Jul 23 2013 Quick search for 3.14 gets me ads for Dominos. Great success-- theircompetitor, Jul 23 2013 3.14159 returns "Cosine Secant Tangent Sine"...-- lurch, Jul 23 2013 3.2 returns pi, but only in Indiana.-- not_morrison_rm, Jul 23 2013 [+]-- FlyingToaster, Jul 24 2013 I almost get it-- pashute, Jul 25 2013 My favorite constant: 0.739085133215
The problem: If I run a search on 0.739, and there exists a page somewhere on the web that contains the character sequence 0.7391, will existing search engines reliably match it to that search?-- LoriZ, Aug 06 2013 random, halfbakery