/usr/lib/R/site-library/rngtools/INDEX is in r-cran-rngtools 1.2.4-2build1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8  | RNGseed                 Directly Getting or Setting the RNG Seed
RNGseq                  Generate Sequence of Random Streams
RNGstr                  Formatting RNG Information
checkRNG                Checking RNG Differences in Unit Tests
getRNG                  Getting/Setting RNGs
rng.equal               Comparing RNG Settings
rngtools                Utility functions for working with Random
                        Number Generators
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