Jelly, a huge number \$ + 1605\$ bytes
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Ø%*`*`¡*`¡*`¡*`¡*`¡*`¡*`¡*`¡*`¡*`¡*`¡*`¡*`¡*`¡*`¡*`¡*`¡*`¡*`¡*`¡*`¡*`¡*`¡*`¡*`©ç`”.xŒV
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More specifically, this outputs an error message which is 1605 bytes long, plus two occurrences of massive chains of ...
. Unsurprisingly, this does not actually show an error really no matter where you run it, but in theory it will
How it works, and what the number is
The basic strategy is simple: create a massive number, repeat "."
that many times, then run as Python code, throwing a syntax error.
The first line is a helper link which we use to calculate a number with Knuth's up-arrow notation. We're calculating \$z \uparrow^z z\$.
\$z\$ is absolutely huge. For convenience, we'll say \$t = { {2^{32}} ^ {2^{32}} }\$. To start, we'll take
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This yields \$u_t\$ where
$$u_0 = t \\ u_n = u_{n-1}^{u_{n-1}}$$
We then take the related value \$u'_t\$ where
$$u'_0 = t, u'_1 = u_t, u'_2 = u_{u_t}, \dots$$
then \$u''_t\$ where
$$u''_0 = t, u''_1 = u'_t, u''_2 = u'_{u'_t}, \dots$$
and so on, until \$x = u''''''''''''''''''''''''_t\$ (that's 24 \${}'\$s).
Finally, we yield \$z = x^x\$ and calculate \$z \uparrow^z z\$.