/usr/include/ngram/ is in libngram-dev 1.3.2-3.
This file is owned by root:root, with mode 0o755.
..
/usr/include/ngram/hist-arc.h
/usr/include/ngram/hist-mapper.h
/usr/include/ngram/lexicographic-map.h
/usr/include/ngram/ngram-absolute.h
/usr/include/ngram/ngram-bayes-model-merge.h
/usr/include/ngram/ngram-complete.h
/usr/include/ngram/ngram-context-merge.h
/usr/include/ngram/ngram-context-prune.h
/usr/include/ngram/ngram-context.h
/usr/include/ngram/ngram-count-merge.h
/usr/include/ngram/ngram-count-of-counts.h
/usr/include/ngram/ngram-count-prune.h
/usr/include/ngram/ngram-count.h
/usr/include/ngram/ngram-hist-merge.h
/usr/include/ngram/ngram-input.h
/usr/include/ngram/ngram-katz.h
/usr/include/ngram/ngram-kneser-ney.h
/usr/include/ngram/ngram-make.h
/usr/include/ngram/ngram-marginalize.h
/usr/include/ngram/ngram-merge.h
/usr/include/ngram/ngram-model-merge.h
/usr/include/ngram/ngram-model.h
/usr/include/ngram/ngram-mutable-model.h
/usr/include/ngram/ngram-output.h
/usr/include/ngram/ngram-randgen.h
/usr/include/ngram/ngram-relentropy.h
/usr/include/ngram/ngram-seymore-shrink.h
/usr/include/ngram/ngram-shrink.h
/usr/include/ngram/ngram-split.h
/usr/include/ngram/ngram-transfer.h
/usr/include/ngram/ngram-unsmoothed.h
/usr/include/ngram/ngram-witten-bell.h
/usr/include/ngram/ngram.h
/usr/include/ngram/util.h