What's this function by Ramanujan? In this paper by Ramanujan (http://ramanujan.sirinudi.org/Volumes/published/ram32.pdf), he writes the following formula:
$$[x] = \pi_1(x) + \pi_2(x) + \pi_3(x) + \cdots ,$$
what exactly is the function on the LHS? Is it the floor function?

The  LHS is the floor function, the RHS is $\pi_k(x)$,  the number of positive integers which do not exceed $x$ and have exactly $k$ prime factors. 
