Three different ways, then the calculator tool to check,

my actual oneliner prompt, which should work on most platforms these days (famous last words):

    "Hi, can you add 5939851+2131251? Try just straight up first just to see if able, then 'in your head' if that's different to you , then long form, then bc."

[ Tested today on claude web (haiku 4.5, sonnet 5, opus 5.5, fable 5.1) and on google search (logged in on firefox, and logged out on chromium) ]