In "Life lessons" http://www.theguardian.com/science/2005/apr/07/science.highereducation?fb_ref=desktop The Guardian (7 April 2005)
“The obvious mathematical breakthrough would be development of an easy way to factor large prime numbers.”
Source: The Road Ahead (1995), p. 265 in hardcover edition, corrected in paperback
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General System Theory (1968), 4. Advances in General Systems Theory

Problema, numeros primos a compositis dignoscendi, hosque in factores suos primos resolvendi, ad gravissima ac utilissima totius arithmeticae pertinere, et geometrarum tum veterum tum recentiorum industriam ac sagacitatem occupavisse, tam notum est, ut de hac re copiose loqui superfluum foret. … [P]raetereaque scientiae dignitas requirere videtur, ut omnia subsidia ad solutionem problematis tam elegantis ac celebris sedulo excolantur.
Disquisitiones Arithmeticae (1801): Article 329
Oskar Morgenstern (Mathematica/Mathematic Policy Research), (from "A Look Back at Some of Our Contributions Over Time")

Statement of Poisson's law also known as the Law of Large Numbers (1837), as quoted by [Richard Von Mises, Probability, Statistics and Truth, Allen and Unwin, 1957, 104-105]

Source: The lever of riches: Technological creativity and economic progress, 1992, p. 14

"The Role of Mathematics in the Sciences and in Society" (1954) an address to Princeton alumni, published in John von Neumann : Collected Works (1963) edited by A. H. Taub <!-- Macmillan, New York -->; also quoted in Out of the Mouths of Mathematicians : A Quotation Book for Philomaths (1993) by R. Schmalz
Context: A large part of mathematics which becomes useful developed with absolutely no desire to be useful, and in a situation where nobody could possibly know in what area it would become useful; and there were no general indications that it ever would be so. By and large it is uniformly true in mathematics that there is a time lapse between a mathematical discovery and the moment when it is useful; and that this lapse of time can be anything from 30 to 100 years, in some cases even more; and that the whole system seems to function without any direction, without any reference to usefulness, and without any desire to do things which are useful.
2.4, "Discrete Mathematics and the Notion of Infinity", p. 45
The Forgotten Revolution: How Science Was Born in 300 BC and Why It Had to Be Reborn (2004)

Source: Adventures of a Mathematician - Third Edition (1991), Chapter 15, Random Reflections on Mathematics and Science, p. 277

W. E. Lamb, Super classical quantum mechanics: the best interpretation of non relativistic quantum mechanics, Am. J. Phys. 69, 413-422 (2001).