Comparing $\frac{(x+n)!}{x!}$ to $n!$

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  • Let $n \ge 2$ be an integer and $p$ be a prime that divides $n!$.

  • Let $x \ge n$ be an integer.

  • Let $v_p(u)$ be the highest power of $p$ that divides $u$.

It is well known that $n!$ divides $\dfrac{(x+n)!}{x!}$.

Let $x+j$ be the integer in the sequence $\{x+1, x+2, \dots, x+n\}$ divisible by the highest power of $p$.

Does it follow that $v_p(x+j) \ge v_p({{x+n}\choose{n}})$?

I am thinking that the answer is yes.

Here's my thinking:

(1) Let $p^t$ be the highest power of $p$ in the sequence ${x+1, x+2, \dots, x+n}$.

(2) Using Legendre's Formula, it is well known that $p^{v_p({{x+n}\choose{n}})} \le x+n$ [See see this paper for the argument].

(3) So, $v_p({{x+n} \choose {x}}) \le t$ and $p^{v_p\left({{x+n} \choose {x}}\right)}$ necessarily divides $x+j$.


Edit: Cleaning up the question. I think that much of my original assumptions are unnecessary.


Edit 2: @Mathlove points out a mistake in my reasoning. For $x=5, n=4, p=2$ for example, $v_p\left({{x+n}\choose{x}}\right) < t$

This is consistent with my conclusion even if it changes the details of my argument.

This question relates to step(6) in a previous question.