Problem installing R 3.4 in Ubuntu 16.04

Hello,

I'm trying to install R version 3.4 in Ubuntu 16.04 by following the
instructions here:
https://cloud.r-project.org/bin/linux/ubuntu/README.html

First, I added the line 'deb https://cloud.r-project.org/bin/linux/ubunutu
xenial/' to sources.list.

Next I ran the following command:
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys
E298A3A825C0D65DFD57CBB651716619E084DAB9
This seemed to work fine.

But when I then ran sudo apt-get update, I got the following output (I'm
omitting earlier lines that looked okay):
Err:7 https://cloud.r-project.org/bin/linux/ubunutu xenial/ Packages
  404  Not Found
Ign:8 https://cloud.r-project.org/bin/linux/ubunutu xenial/
Translation-en_US
Ign:9 https://cloud.r-project.org/bin/linux/ubunutu xenial/ Translation-en
Fetched 323 kB in 2s (116 kB/s)
Reading package lists... Done
W: The repository 'https://cloud.r-project.org/bin/linux/ubunutu 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
https://cloud.r-project.org/bin/linux/ubunutu/xenial/Packages  404  Not
Found
E: Some index files failed to download. They have been ignored, or old ones
used instead.

If I then run sudo apt-get install r-base, the version that gets installed
is 3.2.3.

Can someone give me pointers on what I'm doing wrong here?

Thanks very much,
Jason Murcko