Turn-ons: game theory, combinatorics, probability, progressive rock.
Turn-offs: that feeling when someone rubs paper on chalkboard.

Algorithm to compute number ordered selections w/ upper bound restrictions:
https://math.stackexchange.com/questions/4277678/permutation-of-a-subset-from-a-set-with-multiple-repetitions

Unordered version:
https://math.stackexchange.com/questions/4270053/time-complexity-of-number-of-solutions-to-equation-of-varying-size-with-varying/4270328#4270328

Zeilberger quick how-to:https://math.stackexchange.com/a/4322239

How to ask a good question advice: https://math.meta.stackexchange.com/a/34067