RE: Some pattern that I used to know

[...] the human brain is monumentally lazy [...]

Try "super duper efficient". You wouldn't be able to be active for more than an hour a day otherwise. I know you know, but, ya know.

number as the numerals "31" in base 10. Interesting point which I always like to bring up is that there is an actual number behind the representation that is independent of the representation. Looking at other bases is the best way to see this.Also on the number itself. As @abh12345 pointed out the numerals "11111" in base 2 (binary) is the same

The representation can however give the lazy / efficient brain some quick summary clues as to the nature of the number. What we get from "11111" is an idea of the log 10 magnitude (i.e. that it's between 10^6 and 10^6) just from the amount of numerals. It also has a good chance of being a prime number, because roughly a quarter of known primes end in 1, and there is on average a prime every 10.4 numbers up to 100k. As it happens, it's not a prime, the closest are 11093 and 11113.

Otherwise it's pure brain pattern, like how the wheel of a vehicle in motion appears to be still in video playback when it's rate divides "evenly" with the frame rate of a video recorder.