Err:12 http://ppa.launchpad.net/blk/ppa/ubuntu xenial/main amd64 Packages
  404  Not Found
Err:13 http://ppa.launchpad.net/blk/ppa/ubuntu xenial/main i386 Packages
  404  Not Found
Ign:14 http://ppa.launchpad.net/blk/ppa/ubuntu xenial/main all Packages
Ign:15 http://ppa.launchpad.net/blk/ppa/ubuntu xenial/main amd64 DEP-11 Metadata
Ign:16 http://ppa.launchpad.net/blk/ppa/ubuntu xenial/main DEP-11 64x64 Icons
Err:17 http://ppa.launchpad.net/niko2040/e19/ubuntu xenial/main amd64 Packages
  404  Not Found
Err:18 http://ppa.launchpad.net/niko2040/e19/ubuntu xenial/main i386 Packages
  404  Not Found
Ign:19 http://ppa.launchpad.net/niko2040/e19/ubuntu xenial/main all Packages
Ign:20 http://ppa.launchpad.net/niko2040/e19/ubuntu xenial/main amd64 DEP-11 Metadata
Ign:21 http://ppa.launchpad.net/niko2040/e19/ubuntu xenial/main DEP-11 64x64 Icons
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Reading package lists... Done
W: The repository 'http://ppa.launchpad.net/blk/ppa/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.
W: The repository 'http://ppa.launchpad.net/niko2040/e19/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/blk/ppa/ubuntu/dists/xenial/main/binary-amd64/Packages  404  Not Found
E: Failed to fetch http://ppa.launchpad.net/blk/ppa/ubuntu/dists/xenial/main/binary-i386/Packages  404  Not Found
E: Failed to fetch http://ppa.launchpad.net/niko2040/e19/ubuntu/dists/xenial/main/binary-amd64/Packages  404  Not Found
E: Failed to fetch http://ppa.launchpad.net/niko2040/e19/ubuntu/dists/xenial/main/binary-i386/Packages  404  Not Found
E: Some index files failed to download. They have been ignored, or old ones used instead.
amaury@amaury-M15x:~$