Administrator list

You can create a group and add all sys admins using a membership rule.

In the designers Groups systems admins are added directly when you create an account in appian. 

In designers group basic users can also be there . They don't have the admin access but they can access the o applications with necessary permissions in the application.

Below code will help you to get the list of admin users. 

a!localVariables(
  local!users: getallusers(0,-1),
  reject(fn!isnull,a!forEach(
    items: local!users,
    expression: if(
      user(fv!item,"userTypeName")="Administrator",
      fv!item,
      null()
    )
  ))
)

Hello Purvaja 

https://community.appian.com/b/appmarket/posts/people-functions---plug-in

Install(Deploy) the "People Functions" plugin from the Appian Marketplace.
Use the getAllUsers() function to retrieve all users.
Iterate through the users and use isUserSystemAdministrator() function to identify admins.