19 looked sophisticated, a calm mature lion or an eagle flying high. 17 looked like a very sharp shark or a young powerful wolf.
However, 17 was superior to 18 in my mind aesthetically, not numerically. If you'd make me choose between receiving $18MM or $17MM, I'm not above receiving an extra one.
Like for instance, in high-school when learning derivation and integration.. I'd always imagine sine to be a dominant almost bullying function (starts with an "S", looks erect like a snake about to jump at you), and cosine to be the submissive one (starts with a C, curved back). In many ways, the Sine behaves like a treacherous snake you have to handle more carefully than a Cosine.
Some formulas invoked musical tones and melodies in my mind (like the integration by parts has a specific melody I can hear).
The Sarrus method for calculating determinants was always the difference of two stars of David.
Other things are almost muscular. I used to know every phone number in my contact list for it only existed in my head (pushed numbers when I wanted to call someone). I remembered the numbers because the thumb followed a certain pattern on the keypad and each pattern was unique. Sometimes someone's phone number evoked things that were pertinent about the person.