...

Underneath the painting with the room with no windows or doors

It doubles, and one more

2 5 26 677 ...

"Room with no windows... ah! focus! this is not the time for scary memories!"

"I think I've only seen 2 paintings here. Most of the frames have photos"

"Theres 4 paintings, actually"

"Did you take a picture of them?"

"Of course! Let me search"

"She can and will fill your phone's memory just sending photos of things she likes"

"Delete them then?"

"No"

"Are you talking shit about me to the new guy?"

"Not at all!"

"Ah! These are the paintings"

"Oh, I get it now"

"Under one of these paintings, there must be some kind of pad or lock where you can put the number that has been crossed over here.

Whoever wrote this probably couldn't memorize which painting and which number it was, so, here's a post-it note they could carry around.

And seeing as these things can get easily lost, they decided to encrypt it in a silly children's riddle and some math sequence.

I think most people would just ignore it or not bother to solve it. Not me though. I really like puzzles."

"What was that word again? Hyperfix something?"

"Although this could just be just a silly riddle that leads nowhere. I mean, if they needed to write something down, why not a phone?"

"Wait, so you got the answer already? That's impressive!"

"Yeah! Who cares if it's just some kid's game? Let's find out!"

"Oh, um, thank you."