A friend told me he's going to get a tattoo with "頑張".
頑張 doesn't exist on the dictionary without its -る conjugating part, so is it grammatically correct using it alone, as if it was a noun? Does it make any sense? More generally, does it make any sense omitting the conjugating part from a two (or more) kanji verb and using it as a noun? Wouldn't it be better to use the 連用形 form? Should I suggest my friend to rather get a "頑張り" tattoo?
Thank you for your help!