$ sudo yum install nodejs npm --enablerepo=epel

を実行したら

Loaded plugins: extras_suggestions, langpacks, priorities, update-motd
Repository nodesource is listed more than once in the configuration
Repository nodesource-source is listed more than once in the configuration
amzn2-core                                                                | 2.4 kB  00:00:00     
224 packages excluded due to repository priority protections
Resolving Dependencies
--> Running transaction check
---> Package nodejs.x86_64 2:6.17.1-1nodesource will be installed
---> Package npm.x86_64 1:3.10.10-1.6.17.1.1.el7 will be installed
--> Processing Dependency: nodejs = 1:6.17.1-1.el7 for package: 1:npm-3.10.10-1.6.17.1.1.el7.x86_64
--> Finished Dependency Resolution
Error: Package: 1:npm-3.10.10-1.6.17.1.1.el7.x86_64 (epel)
           Requires: nodejs = 1:6.17.1-1.el7
           Available: nodejs-6.0.0-1nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 6.0.0-1nodesource.el7.centos
           Available: nodejs-6.1.0-1nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 6.1.0-1nodesource.el7.centos
           Available: nodejs-6.2.0-1nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 6.2.0-1nodesource.el7.centos
           Available: nodejs-6.2.1-1nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 6.2.1-1nodesource.el7.centos
           Available: nodejs-6.2.2-1nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 6.2.2-1nodesource.el7.centos
           Available: 1:nodejs-6.3.0-1nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 1:6.3.0-1nodesource.el7.centos
           Available: 1:nodejs-6.3.1-1nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 1:6.3.1-1nodesource.el7.centos
           Available: 1:nodejs-6.4.0-1nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 1:6.4.0-1nodesource.el7.centos
           Available: 1:nodejs-6.6.0-1nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 1:6.6.0-1nodesource.el7.centos
           Available: 1:nodejs-6.7.0-1nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 1:6.7.0-1nodesource.el7.centos
           Available: 1:nodejs-6.17.1-1.el7.x86_64 (epel)
               nodejs = 1:6.17.1-1.el7
           Available: 2:nodejs-6.8.0-1nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 2:6.8.0-1nodesource.el7.centos
           Available: 2:nodejs-6.8.1-1nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 2:6.8.1-1nodesource.el7.centos
           Available: 2:nodejs-6.9.0-1nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 2:6.9.0-1nodesource.el7.centos
           Available: 2:nodejs-6.9.1-1nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 2:6.9.1-1nodesource.el7.centos
           Available: 2:nodejs-6.9.2-1nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 2:6.9.2-1nodesource.el7.centos
           Available: 2:nodejs-6.9.3-1nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 2:6.9.3-1nodesource.el7.centos
           Available: 2:nodejs-6.9.4-1nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 2:6.9.4-1nodesource.el7.centos
           Available: 2:nodejs-6.9.5-1nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 2:6.9.5-1nodesource.el7.centos
           Available: 2:nodejs-6.10.0-1nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 2:6.10.0-1nodesource.el7.centos
           Available: 2:nodejs-6.10.1-1nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 2:6.10.1-1nodesource.el7.centos
           Available: 2:nodejs-6.10.2-1nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 2:6.10.2-1nodesource.el7.centos
           Available: 2:nodejs-6.10.2-2nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 2:6.10.2-2nodesource.el7.centos
           Available: 2:nodejs-6.10.3-1nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 2:6.10.3-1nodesource.el7.centos
           Available: 2:nodejs-6.11.0-1nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 2:6.11.0-1nodesource.el7.centos
           Available: 2:nodejs-6.11.1-1nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 2:6.11.1-1nodesource.el7.centos
           Available: 2:nodejs-6.11.2-1nodesource.el7.centos.x86_64 (nodesource)
               nodejs = 2:6.11.2-1nodesource.el7.centos
           Available: 2:nodejs-6.11.3-1nodesource.x86_64 (nodesource)
               nodejs = 2:6.11.3-1nodesource
           Available: 2:nodejs-6.11.4-1nodesource.x86_64 (nodesource)
               nodejs = 2:6.11.4-1nodesource
           Available: 2:nodejs-6.11.5-1nodesource.x86_64 (nodesource)
               nodejs = 2:6.11.5-1nodesource
           Available: 2:nodejs-6.12.0-1nodesource.x86_64 (nodesource)
               nodejs = 2:6.12.0-1nodesource
           Available: 2:nodejs-6.12.1-1nodesource.x86_64 (nodesource)
               nodejs = 2:6.12.1-1nodesource
           Available: 2:nodejs-6.12.2-1nodesource.x86_64 (nodesource)
               nodejs = 2:6.12.2-1nodesource
           Available: 2:nodejs-6.13.0-1nodesource.x86_64 (nodesource)
               nodejs = 2:6.13.0-1nodesource
           Available: 2:nodejs-6.13.1-1nodesource.x86_64 (nodesource)
               nodejs = 2:6.13.1-1nodesource
           Available: 2:nodejs-6.14.0-1nodesource.x86_64 (nodesource)
               nodejs = 2:6.14.0-1nodesource
           Available: 2:nodejs-6.14.1-1nodesource.x86_64 (nodesource)
               nodejs = 2:6.14.1-1nodesource
           Available: 2:nodejs-6.14.2-1nodesource.x86_64 (nodesource)
               nodejs = 2:6.14.2-1nodesource
           Available: 2:nodejs-6.14.3-1nodesource.x86_64 (nodesource)
               nodejs = 2:6.14.3-1nodesource
           Available: 2:nodejs-6.14.4-1nodesource.x86_64 (nodesource)
               nodejs = 2:6.14.4-1nodesource
           Available: 2:nodejs-6.15.0-1nodesource.x86_64 (nodesource)
               nodejs = 2:6.15.0-1nodesource
           Available: 2:nodejs-6.15.1-1nodesource.x86_64 (nodesource)
               nodejs = 2:6.15.1-1nodesource
           Available: 2:nodejs-6.16.0-1nodesource.x86_64 (nodesource)
               nodejs = 2:6.16.0-1nodesource
           Available: 2:nodejs-6.17.0-1nodesource.x86_64 (nodesource)
               nodejs = 2:6.17.0-1nodesource
           Installing: 2:nodejs-6.17.1-1nodesource.x86_64 (nodesource)
               nodejs = 2:6.17.1-1nodesource
 You could try using --skip-broken to work around the problem
 You could try running: rpm -Va --nofiles --nodigest

と怒られた。

$ sudo yum install nodejs npm --enablerepo=epel --skip-broken

で解決。

$ npm -v
# バージョンが出ればOK