given a prime, finding where it is the list of primes

edit

prime_pi?
Type:           PrimePi
String form:    prime_pi
File:           /usr/local/sage-8/local/lib/python2.7/site-packages/sage/functions/prime_pi.pyx
Docstring:     
   The prime counting function, which counts the number of primes less
   than or equal to a given value.

   INPUT:

   * "x" - a real number

   * "prime_bound" - (default 0) a real number < 2^32, "prime_pi"
     will make sure to use all the primes up to "prime_bound"
     (although, possibly more) in computing "prime_pi", this can
     potentially speedup the time of computation, at a cost to memory
     usage.

   OUTPUT:

   integer -- the number of primes <= "x"

So, given your number x,an obvious "brute-force" one-liner is :

def foo(x): return map(lambda(t):prime_pi(t[0],sqrt(x)), factor(x))
bar=Integer(round(10^10*random()))
bar
7218184858
foo(bar)
[1, 1211, 31354]

HTH,