This number is a prime.
The largest prime denominator of a π approximation obtainable using double precision floating point on a 32-bit PC such that the error is in the 17th digit. The corresponding numerator is 325994779. The log of the proportionate error plus the logs of the numerator and the denominator is negative, as is the case with the well known approximations 22/7 and 355/113. The value of π obtained in this case is 3.141592653589793(1) which is beyond the precision limit of MS Excel. [Croll]