What is the best play strategy for a game called "21"?

I recommend looking at the game "Nim" like Sean Xie suggested. https://www.archimedes-lab.org/How_to_Solve/Win_at_Nim.html or https://boardgamestrategy.blog/2017/02/13/counting-to-21-strategy/

As the number of players increase, however, there less of a strategy (except in extreme cases) because the other players can cooperate against you; they have a wider range of options, collectively, than you do, so you can't use the sort of strategy that you can use in the two-player version.

convergence of the series $\sum_{n=1}^{\infty}(1/n^{\alpha})(\int_{0}^{\frac{\pi}{4}}\tan^{n}tdt)x^{n}$

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Defining joint distribution of two uniform variables where one is bounded by the other

Finding $T^{\perp}$!

Order of convergence of the sequence $\{x_n\}_{n=0}^{\infty }$ given by $x_{n+1}=2x_n-\pi {x_n}^2$ with $x_0=1/3$

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Can we define higher-order tangent spaces of a manifold with equivalence classes defined equating second derivatives?

Proving that there is no matrix $B$ for such $By = x$

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Is my process of doing this math accurate?

Rewriting triple integrals rectangular, cylindrical, and spherical coordinates