"a" or "an" with big O notation? A simple (though somewhat pedantic) question: when using big O notation in a sentence, should it be preceded with "a" or "an"?  Example:


  The extra loop results in a/an $\mathcal{O}(N)$ increase in cost.


The ubiquitous Cormen textbook notes on page 47:


  For a given function $g(n)$, we denote by $\mathcal{O}(g(n))$ (pronounced “big-oh of g of n” or sometimes just “oh of g of n”)


which would seem to indicate "a" should precede something pronounced "big-oh".  Later on the same page, however, the textbook uses the phrase "an $\mathcal{O}(n^2)$ upper bound."   Which is used more in the literature?  It seems like a triviality, but as someone working on the edge of theoretical computer science from a primary focus on another field, I'd like not to sound like an outsider.
Evidence for "an":


Ajtai, Miklós, János Komlós, and Endre Szemerédi. "An O(n log n) sorting network." Proceedings of the fifteenth annual ACM symposium on Theory of computing. ACM, 1983.
Asadpour, Arash, et al. "An O(log n/log log n)-approximation Algorithm for the Asymmetric Traveling Salesman Problem." SODA. Vol. 10. 2010.
Bracha, Gabriel. "An O(log n) expected rounds randomized Byzantine generals protocol." Journal of the ACM (JACM) 34.4 (1987): 910-920.
Hwang, F. K. "An O(n log n) algorithm for suboptimal rectilinear Steiner trees." Circuits and Systems, IEEE Transactions on 26.1 (1979): 75-77.
Tarjan, Robert E., and Christopher J. Van Wyk. "An O(n log log n)-time algorithm for triangulating a simple polygon." SIAM Journal on Computing 17.1 (1988): 143-178.
Yao, Andrew Chi-Chih. "An O (|E| log log|V|) algorithm for finding minimum spanning trees." Information Processing Letters 4.1 (1975): 21-23.


Of course, these examples alone merely suggest that "an" is acceptable. This list does not show that "an" is necessarily standard or preferred nor does it show that "a" is unacceptable.