Description: The prime-counting function ppi at 2 . (Contributed by Mario Carneiro, 21-Sep-2014)
Ref | Expression | ||
---|---|---|---|
Assertion | ppi2 | |- ( ppi ` 2 ) = 1 |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | 1nn0 | |- 1 e. NN0 |
|
2 | df-2 | |- 2 = ( 1 + 1 ) |
|
3 | ppi1 | |- ( ppi ` 1 ) = 0 |
|
4 | 2prm | |- 2 e. Prime |
|
5 | 1 2 3 4 | ppi1i | |- ( ppi ` 2 ) = ( 0 + 1 ) |
6 | 1e0p1 | |- 1 = ( 0 + 1 ) |
|
7 | 5 6 | eqtr4i | |- ( ppi ` 2 ) = 1 |