Mathematical and Physical Journal
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Problem B. 4357. (April 2011)

B. 4357. Let n>1 be a positive integer. Show that n3-n2 is a factor of the binomial coefficient \binom{n^2}{n+1}.

(Suggested by G. Holló, Budapest)

(3 pont)

Deadline expired on May 10, 2011.

Sorry, the solution is available only in Hungarian. Google translation

Megoldás. A szóban forgó oszthatóság leolvasható az

\(\displaystyle \binom{n^2}{n+1}= \frac{n^2(n^2-1)(n^2-2)\cdots(n^2-n)}{(n+1)n(n-1)\cdots1}= \)

\(\displaystyle =\frac{n^2(n^2-1)(n^2-n)}{(n+1)n(n-1)}\cdot \frac{(n^2-2)\cdots(n^2-n+1)}{(n-2)\cdots1} =(n^3-n^2)\dbinom{n^2-2}{n-2}\)



73 students sent a solution.
3 points:55 students.
2 points:14 students.
1 point:4 students.

Problems in Mathematics of KöMaL, April 2011