Primorial, (n#)

[quinn]

I only am wondering about the Primorial function, n#, (product of all primes less than or equal to n)

The gamma/factorial function has a nice recursive relationship that is composed of elementary functions; does there exsist an extension to the primorial function?

[shmoe]

There's a simple asymptotic for it's logarithm given by one form of the prime number theorem, log(n#)~n.

[Karlisbad]

If you define the Chebyshev function:

\theta (x)= \sum_{p<x} log(p) then:

\theta (p_{n}) = log(p#) but using this definition the PNT gives

log(p # ) \sim nlogn

[CRGreathouse]

p# is about e^p. Pierre Dusart has a paper with fairly tight bounds for this and other functions relating to prime counting.