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I recently came across a number of the form $$ (\log\alpha)(\log\beta) $$ where $\alpha$ and $\beta$ were integers greater than 1. I wondered if the product was transcendental. Can this be proved? The natural next step would be $\alpha,\beta$ algebraic other than 0,1 (but I can’t even show the integer case so this is hopeless for me).

I was thinking in particular about A341577 but the problem is of course much more general, and I couldn't see a way to solve this with just the usual tools.

Charles
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2 Answers2

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You can show unconditionally that the logarithms $\log p$ of the primes are linearly independent over $\mathbb{Q}$; this is equivalent to unique prime factorization. Given this, Schanuel's conjecture implies that the logarithms $\log p$ of the primes are in fact algebraically independent over $\mathbb{Q}$. This would imply in particular that for integers $n, m$, $\log n \log m$ is transcendental unless $n = 1$ or $m = 1$.

Unfortunately Schanuel's conjecture is, as far as I know, wide open.

Qiaochu Yuan
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If $\log(a)$ here means common log with base 10 then, no product of logs aren't transcendental, a counter example would be- Let's say $a=10$ and $b=100$ Then, $\log(a)=1$ and $\log(b)=2$ which are roots of $x^2-3x+2=0$

However if $\ln$ is taken log with base e then, $\ln(n)$ is transcendental for all $n>1$ where $n$ is non transcendental

Is ln(n) transcendental for all integer $n > 1$? You can get why $\ln(n)$ is transcendental here.

then, $\ln(a).\ln(b)$ has to be transcendental for all $a,b>1$ where $a,b$ are integers.As $\ln a$ and $\ln b$ are transcendental their product is as well.

(Product of $2$ transcendental not transcendental when the transcendental term gets cut like in $\frac{e^1}{e}$ one is the reciprocal of the other and $\ln x$ and $\frac{a}{\ln x}$ (a being any algebraic no.) don't intersect so not $\ln a$ not equal to $\frac{a}{b}$).

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    -1 The last line is not true. EG The product of $ e, 2/e$ is not transcendental, even though the two are not reciprocal of each other. – Calvin Lin Nov 22 '24 at 03:57
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    I see a gap in your reasoning: How exactly did you conclude that $\ln(a)\ln(b)$ is transcendental for all positive integers $a, b$? Which results did you use to derive that? – Duong Ngo Nov 22 '24 at 04:10
  • The reciprocal thing was not absolute I put it there as an example of when will product of 2 transcendental no. be non transcendental. It will be non transcendental when the transcendental term gets cut as in e and 2/e it's the same thing. – Yashasvi Bansode Nov 22 '24 at 04:29
  • Obviously if $k$ is transcendental and $\frac qk$ where $q$ is not have a non transcendental product is trivial. But if $k$ and $w$ are two "unrelated" transcendental numbers we really have no test to know if the product is or is not transcendental. It is not true of obvious that as they "aren't related" their transcendence won't "cancel out". Your conclusion is simply wrong and we do not know (we really do not-- it is an unsolved problem) if the product of logs will be transcendent. – fleablood Nov 22 '24 at 05:15