# [Lua], 64 bytes

<!-- language-all: lang-lua -->

    s="abcdefghijklmnopqrstuvwxyz"print(s..s:upper().."_0123456789")

[Try it online!][TIO-kzvqx3el]

[Lua]: https://www.lua.org/
[TIO-kzvqx3el]: https://tio.run/##yylN/P@/2FYpMSk5JTUtPSMzKzsnNy@/oLCouKS0rLyiskqpoCgzr0SjWE@v2Kq0oCC1SENTT08p3sDQyNjE1MzcwlJJ8/9/AA "Lua – Try It Online"