Get follower IDs of user.

gettwitterfollowers.rb

require 'twitter'

client = Twitter::REST::Client.new do |config|
  config.consumer_key        = "..."
  config.consumer_secret     = "..."
  config.access_token        = "..."
  config.access_token_secret = "..."
end
user = 123
cursor = client.follower_ids(user, count: 5000)
cursor.each do |item|
  puts item
end