Trying to install mathoid through the official ubuntu package on Ubuntu 16.04 gets me this result:
sudo apt-get update Ign:1 http://linux.dropbox.com/ubuntu xenial InRelease Ign:2 http://linux.dropbox.com/ubuntu wily InRelease Hit:3 http://security.ubuntu.com/ubuntu xenial-security InRelease Hit:4 http://linux.dropbox.com/ubuntu xenial Release Hit:5 http://linux.dropbox.com/ubuntu wily Release Hit:6 http://apt.galliumos.org xenon InRelease Hit:8 http://ppa.launchpad.net/nathan-renniewaldock/flux/ubuntu xenial InRelease Hit:9 http://repo.sinew.in stable InRelease Hit:10 http://archive.ubuntu.com/ubuntu xenial InRelease Hit:12 https://releases.wikimedia.org/debian jessie-mediawiki InRelease Ign:13 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial InRelease Hit:14 http://archive.ubuntu.com/ubuntu xenial-updates InRelease Ign:15 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial Release Ign:16 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial/main amd64 Packages Ign:17 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial/main all Packages Ign:18 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial/main Translation-en_US Ign:19 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial/main Translation-en Ign:16 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial/main amd64 Packages Ign:17 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial/main all Packages Ign:18 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial/main Translation-en_US Ign:19 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial/main Translation-en Ign:16 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial/main amd64 Packages Ign:17 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial/main all Packages Ign:18 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial/main Translation-en_US Ign:19 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial/main Translation-en Ign:16 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial/main amd64 Packages Ign:17 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial/main all Packages Ign:18 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial/main Translation-en_US Ign:19 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial/main Translation-en Ign:16 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial/main amd64 Packages Ign:17 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial/main all Packages Ign:18 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial/main Translation-en_US Ign:19 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial/main Translation-en Err:16 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial/main amd64 Packages 404 Not Found Ign:17 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial/main all Packages Ign:18 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial/main Translation-en_US Ign:19 http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial/main Translation-en Reading package lists... Done W: The repository 'http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu xenial Release' does not have a Release file. N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use. N: See apt-secure(8) manpage for repository creation and user configuration details. E: Failed to fetch http://ppa.launchpad.net/physikerwelt/mathoid/ubuntu/dists/xenial/main/binary-amd64/Packages 404 Not Found E: Some index files failed to download. They have been ignored, or old ones used instead.