It is believed, and often cited, that in relation to the Collatz conjecture Paul Erdos once said "Mathematics is not yet ready for such problems". However, I have not found any credible reference for this. Is it rumor, common misconception or the truth?
An annotated bibliography by Lagarias on the 3x+1 problem shows a couple mentions of papers by Erdős that touch on related topics, but seems to trace the quote as follows:
- Richard K. Guy (1983a) Don’t try to solve these problems!, Amer. Math. Monthly 90 (1983), 35–41.
The article gives some brief history of work on the 3x + 1 problem. It mentions at second hand a statement of P. Erdős regarding the 3x + 1 problem: “Mathematics is not yet ripe enough for such questions.”
The standard form of the quote, “Mathematics is not yet ready for such problems,” appears to come from an article by the same Lagarias, The 3x+1 Problem and its Generalizations (1985, PDF from the publisher), and the dates are sufficient that he might be misquoting the above reference, so I would take his later bibliography as authoritative: I am guessing that he was somewhat bugged by this quote, too, and that this was the earliest reference he could find to it.