While optimizing my site for the keyword "second mortgage", which appears in the first page results on Google, the phrase 2nd mortgage also happened to rank well.

An interesting discovery, especially considering that page did not include the term 2nd mortgage. The keyword was later added to the page in a couple of places, which improved the ranking. There was also an increase in the search results for similar long tail phrases like, 2nd mortgage loans and 2nd mortgage rates.

You may have a similar opportunity, if your product or service can include phrases with cardinal numbers, which can be written as words or numerical symbols, such as, one, two, three, or 1, 2, 3. The same applies to phrases that use ordinal numbers, which can also be written as words or symbols, such as, first, second, third, or 1st, 2nd, 3rd.

Some keyword examples might include the phrases: first time, first class, first place, one piece, number one, get one free, two way, two step, two for one, three day, three stooges, four wheeler, four quotes, top ten, million dollar. The numbers in phrases like these can be alternated in your content as words and numerical symbols to optimize for both.

There appears to be a connection in the search engines between alternating keyword numbers as written words and symbols, however, it is important to have other sites and directories link to your topical content, preferably using both types of keywords as anchor text. It could be that the double position for the term second mortgage was partly due to other sites using both words and symbols in their links.

While this is not scientific evidence, just an observation from one site, it may provide food for thought, and perhaps another opportunity to increase your business.