Is it possible to find the position of a prime number online? $2$ is the first prime number.
$3$ is the second.
If I give a prime number such as $1151024046313875220631$, is there any software/website which can give the position of the prime number?
I know there are resources to find $N$th prime. But I am having a hard time finding the reverse.
 A: You can use the function prime_pi in Sage (http://sagemath.org), which is also available for free online at https://sagecell.sagemath.org.   For example, 
   sage: prime_pi(2011)
   305

Like Mathematica, Sage's prime_pi function is too slow to solve your problem above.   It's also somewhat slower than Mathematica's still.  
A: If you have access to Mathematica, PrimePi[x] will give you the number of primes less than x. Combined with PrimeQ, which verifies that x is indeed prime, will give you which prime number x is.
EDIT: I have no idea how long Mathematica would take (or if it could in fact compute it) for a number that high.
A: What you are looking for is the "Prime Counting Function".  The closest thing to it you will find online is Wolfram Alpha:
http://www.wolframalpha.com/examples/PrimeNumbers.html
A: If an approximation suffices, you could use the offset logarithmic integral function.
A: Andrew Booker's Nth prime page is excellent... but it can't handle your example number.
I have custom code that can calculate values up to about 2^64, but your number is larger than that.
Thanks to Dusart [1], we can say that its rank is somewhere between 24244547260299402427 and 24247918127257270377.
If the Riemann Hypothesis is true, then we know by Schoenfeld [2] that its rank is somewhere between 24245911027060346607 and 24245911157987206331.
[1] Pierre Dusart, 'Estimates of Some Functions Over Primes without R.H.', preprint (2010), arXiv:1002.0442
[2] Lowell Schoenfeld, 'Sharper Bounds for the Chebyshev Functions theta(x) and psi(x). II'. Mathematics of Computation, Vol 30, No 134 (Apr 1976), pp. 337-360.
A: For primes smaller than your example you can use Wolfram|Alpha, as Adam S pointed out. Wolfram|Alpha has the prime Pi function:
http://www.wolframalpha.com/input/?i=pi(55252335667)
