References for Legendre's prime-counting function

This question is about Legendre's prime-counting function, the one that can be used to calculate the exact amount of prime numbers that are less than or equal to a given number (as long as the number in question is not too large).

Basically, I'm trying to find references for Legendre's prime-counting function. I searched on the web but I couldn't find many references, except maybe this Wikipedia article and this MathWorld article.

Does anyone have any other references for Legendre's prime-counting function, such as books or journal articles?

• You mean proof or history? The proof is straightforward, just use the inclusion-exclusion principle. Jun 15 '14 at 1:19
• @Ian Ok, so what about history? Jun 15 '14 at 1:23