Pent=5. So, the pentatonic is nothing more than a 5 note scale derived from the diatonic major scale.
As to it's relationship to the blues scale, they are not the same. The pentatonic does not have the most significant "blue note" that defines the major blues scale. That would be the flatted 5th that is often bent between it's corresponding sharp tones So, they are not as similar as many people would make them out to be. Also, there are 6 notes in a blues scale. Though the major blues scale is very similar to the minor pentatonic, it is formulated in relation to the major scale. The blues scale is very close to the minor pentatonic in that it contains all of the same notes, with the addition of the note between the 3rd and 4th interval of the minor pentatonic (the blue note). It is that flatted 5th that is often bent upward to resolution that seperates these two scales. The pentatonic just does not do that. Also, the pentatonic has a major and a minor variation. The blues scale can also have a minor version that deviates completely from the pentatonic.
Also, while extremely similar to the pentatonic, it falls into the family of hexatonic scales. So, while it contains 5 similar notes out of 6 with the pentatonic scale. It is still classified as being more related to the whole-tone scale than the pentatonic (6 notes per octave). But, that is due to it's scale family (hexatonic). Oh well, gotta love theory.