Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ • π ƒ ¹ ² ³ °
 

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Thanks
Okay, if I see anything different I will add it here.
Again, I am looking for alternative names. I finished reading that twelvefold Wikipedia article. Formulae enough.
They are best done with exponential generating functions.
In other words, partial permutation <=> k < n
Yes you're right.
A partial permutation? Is that when you do not use all the elements of the set?
Thank you. The Vietnamese names for them roughly translates to:
Hi;
Thanks, but I stress again that I need the official NAME, not the formulae.
Hi;
And the formula for e is
For k=3, n=5:
Hi;
Choosing k objects from n distinct objects with repetition and order matters is n ^ k
d. For example if k=5, then (a1, a2, a2, a3, a3) would be a solution (repetition allowed), and it would be different from, say, (a1, a2, a3, a2, a3). 