Just out of curiosity:
What is the paper with the largest number of citations in all of mathematics?
I think it is Shannon's A Mathematical Theory of Communication (with its 71025 citations, according to Google Scholar), but I don't know any official sources about this.
What are other papers with a large number of citations?
(I am aware that the number of citations does not measure the importance of a work; this question is only for the sake of curiosity.)
On
Using MathSciNet/Math Reviews would give one way of settling "what is mathematical," but I don't see a way to search for the maximum "citations from references." Perusing the list of top citation recipients from 2014 gives a candidate with 1365 such citations:
MR0370183 (51 #6412) Ambrosetti, Antonio; Rabinowitz, Paul H. Dual variational methods in critical point theory and applications. J. Functional Analysis 14 (1973), 349–381.
The Claude Shannon piece mentioned by Mizar has 829 citations from references in MR.
According to the list in this article, the most cited math paper is "Fuzzy Sets" by Zadeh. But the article also links to the top 100 most-cited papers by Google Scholar's count; the most-cited math paper on that list is "A Mathematical Theory of Communication."