/usr/lib/x86_64-linux-gnu/libdoublefann.so is in libfann-dev 2.2.0+ds-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libdoublefann.so.2
/usr/lib/x86_64-linux-gnu/libdoublefann.so.2