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Exercise 2174Number theory › IrrationalityM1Added 3 Nov 2026

Irrationality of e+ π and πe

#irrationality#e#pi#open problem

Statement

Explain why it is unknown whether e+πe+\pi and eπe\pi are irrational.

Hint

If one of them were rational, then ee and π\pi would be roots of a quadratic, but no such relation is known.

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Solution

Known. ee and π\pi are both irrational (indeed transcendental).

If e+π∈Qe+\pi\in\mathbb{Q}. Then e,πe,\pi are roots of X2−sX+p=0X^2-sX+p=0 where s=e+πs=e+\pi and p=eπp=e\pi. If both s,p∈Qs,p\in\mathbb{Q}, then e,πe,\pi are algebraic — contradiction with transcendence.

But only one is known? Actually, if e+π∈Qe+\pi\in\mathbb{Q}, then ee and π\pi are roots of X2−sX+p=0X^2-sX+p=0 for some pp. But we do not know p=eπp=e\pi is rational.

Open problem. Whether e+πe+\pi and eπe\pi are irrational is open. (However, at most one of them can be rational, since their sum and product being rational would force both to be algebraic.)

Conclusion. These are famous open problems in transcendence theory.