/usr/share/sagemath/ellcurves/rank21 is in sagemath-database-elliptic-curves 0.8-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 | 26112076915897777815571388664430310998157918697219343275140810790098571234096793308930 a 1 [1,1,1,-215843772422443922015169952702159835,-19474361277787151947255961435459054151501792241320535] 21 1
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